A worker labours on Namdaemun, officially called Sungnyemun, or "Great South Gate" in central Seoul, South Korea, August 29, 2016. Picture taken on August 29, 2016. REUTERS/Kim Hong-Ji

Workers rest as they labour on Namdaemun, officially called Sungnyemun, or "Great South Gate" in central Seoul, South Korea, August 29, 2016. Picture taken on August 29, 2016. REUTERS/Kim Hong-Ji

South Korean workers gather in front of Namdaemun, officially called Sungnyemun, or "Great South Gate" during a general strike in Seoul December 28, 2013. About 30,000 South Korean workers attend the rally against government decision to set up a unit to run a high-speed bullet train which they say will lead to privatisation and layoffs. REUTERS/Kim Hong-Ji (SOUTH KOREA - Tags: POLITICS CIVIL UNREST TRANSPORT BUSINESS EMPLOYMENT)

South Korean troops attend a military parade in front of Namdaemun, officially called Sungnyemun, or "Great South Gate" during a ceremony to mark the 65th anniversary of Armed Forces Day on the street in central Seoul October 1, 2013. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: MILITARY ANNIVERSARY)

South Korean troops attend a military parade in front of Namdaemun, officially called Sungnyemun, or "Great South Gate" during a ceremony to mark the 65th anniversary of Armed Forces Day on the street in central Seoul October 1, 2013. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: MILITARY ANNIVERSARY)

South Korean troops attend a military parade in front of Namdaemun, officially called Sungnyemun, or "Great South Gate" during a ceremony to mark the 65th anniversary of Armed Forces Day on the street in central Seoul October 1, 2013. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: MILITARY ANNIVERSARY)

South Korean troops attend a military parade in front of Namdaemun, officially called Sungnyemun, or "Great South Gate" during a ceremony to mark the 65th anniversary of Armed Forces Day on the street in central Seoul October 1, 2013. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: MILITARY ANNIVERSARY)

A South Korean traditional gate guard sounds the opening drum during the reopening ceremony of the landmark Sungnyemun Gate, or Namdaemun Gate, in Seoul May 4, 2013. South Korea on Saturday reopened its ancient Namdaemun gate (South Gate) to the public, five years after the historic landmark in central Seoul was destroyed in an arson attack. REUTERS/Kim Jae-Hwan/Pool (SOUTH KOREA - Tags: POLITICS SOCIETY TRAVEL)

South Korean dancers perform during the reopening ceremony of the landmark Sungnyemun Gate, or Namdaemun Gate, in Seoul May 4, 2013. South Korea on Saturday reopened its ancient Namdaemun gate (South Gate) to the public, five years after the historic landmark in central Seoul was destroyed in an arson attack. REUTERS/Kim Jae-Hwan/Pool (SOUTH KOREA - Tags: POLITICS SOCIETY TRAVEL)

Visitors look at a large-sized lantern featuring South Korea's "National Treasure No. 1", officially called Sungnyemun or "Great South Gate", during the Seoul Lantern Festival at the Cheonggye stream in central Seoul November 4, 2011. The festival will run from November 4 to 20. REUTERS/Jo Yong-Hak (SOUTH KOREA - Tags: SOCIETY TRAVEL TPX IMAGES OF THE DAY)

Vehicles move slowly during snowy weather on a road in front of Dongdaemun or the Great East Gate in Seoul January 4, 2010. Large parts of the Korean peninsula were blanketed with heavy snow on Monday that snarled the rush hour commute in Seoul and caused havoc on the first working day of the new year. REUTERS/Jo Yong-Hak (SOUTH KOREA - Tags: ENVIRONMENT)

Dancers perform during a traditional religious service marking the first anniversary of the fire on Namdaemun, officially called Sungnyemun or "Great South Gate", in front of the restoration site in Seoul February 10, 2009. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10, 2008 by an arsonist. The site was opened to the public to mark the first anniversary of the fire. REUTERS/Jo Yong-Hak (SOUTH KOREA)

A woman hangs a piece of paper with her wish for 'perfect restoration of the fire-damaged Namdaemun', officially called Sungnyemun or "Great South Gate", during the first anniversary of the fire in front of the restoration site in Seoul February 10, 2009. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10, 2008 by an arsonist. The site was opened to the public to mark the first anniversary of the fire. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Visitors look at restoration works at the site of the fire-damaged Namdaemun, officially called Sungnyemun or 'Great South Gate', in Seoul February 10, 2009. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10, 2008 by an arsonist. The site was opened to the public to mark the first anniversary of the fire. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Visitors look at restoration works at the site of the damaged Namdaemun, officially called Sungnyemun or "Great South Gate", in Seoul February 10, 2009. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10, 2008 by an arsonist. The site was opened to the public to mark the first anniversary of the fire. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Visitors look at restoration works at the site of the damaged Namdaemun, officially called Sungnyemun or "Great South Gate", in Seoul February 10, 2009. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10, 2008 by an arsonist. The site was opened to the public to mark the first anniversary of the fire. REUTERS/Jo Yong-Hak (SOUTH KOREA)

A man and his daughter look at restoration works at the site of the damaged Namdaemun, officially called Sungnyemun or "Great South Gate", in Seoul February 10, 2009. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10, 2008 by an arsonist. The site was opened to the public to mark the first anniversary of the fire. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Japan's self-defense army soldiers raise South Korea's national flag in front of a snow sculpture in the shape of South Korea's 'Namdaemun', which was badly damaged by fire in 2008, at a rehearsal for the opening of the 60th Sapporo snow festival, northern island of Japan, February 4, 2009. About 270 snow and ice sculptures are exhibited in the one of Japan's famous winter events which goes on from Feb 5 to 11. REUTERS/Kim Kyung-Hoon (JAPAN)

Fire-fighters stand in front of Dongdaemun, officially called Heunginjimun, or "Great East Gate", after a fire drill in Seoul August 20, 2008. The drill, a part of a South Korea-U.S. combined military exercise Ulchi Freedom Guardian, was carried out on Wednesday in hopes of preventing the damage to cultural properties by fire after the country's 600-year-old gate Namdaemun or "Great South Gate" was destroyed by an arsonist last February. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Fire-fighters splash water on Dongdaemun, officially called Heunginjimun, or "Great East Gate", during a fire drill in Seoul August 20, 2008. The drill, a part of a South Korea-U.S. combined military exercise Ulchi Freedom Guardian, was carried out on Wednesday in hopes of preventing the damage to cultural properties by fire after the country's 600-year-old gate Namdaemun or "Great South Gate" was destroyed by an arsonist last February. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Fire-fighters splash water on Dongdaemun, officially called Heunginjimun, or "Great East Gate", during a fire drill in Seoul August 20, 2008. The drill, a part of a South Korea-U.S. combined military exercise Ulchi Freedom Guardian, was carried out on Wednesday in hopes of preventing the damage to cultural properties by fire after the country's 600-year-old gate Namdaemun or "Great South Gate" was destroyed by an arsonist last February. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Fire-fighters splash water on Dongdaemun, officially called Heunginjimun, or "Great East Gate", during an fire drill in Seoul August 20, 2008. The drill, a part of a South Korea-U.S. combined military exercise Ulchi Freedom Guardian, was carried out on Wednesday in hopes of preventing the damage to cultural properties by fire after the country's 600-year-old gate Namdaemun or "Great South Gate" was destroyed by an arsonist last February. REUTERS/Jo Yong-Hak (SOUTH KOREA)

A shaman holding knifes performs during a memorial service for the Namdaemun, officially called Sungnyemun, or "Great South Gate", in front of the fire-damaged gate in Seoul February 18, 2008. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10 by a 70-year-old arsonist who was angry about a compensation payment. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Dancers perform during a memorial service for the Namdaemun, officially called Sungnyemun, or "Great South Gate", in front of the fire-damaged gate in Seoul February 18, 2008. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10 by a 70-year-old arsonist who was angry about a compensation payment. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Dancers perform during a memorial service for the Namdaemun, officially called Sungnyemun, or "Great South Gate", in Seoul February 18, 2008. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10 by a 70-year-old arsonist who was angry about a compensation payment. REUTERS/Jo Yong-Hak (SOUTH KOREA)

People holding artificial flowers attend a memorial service for the Namdaemun, officially called Sungnyemun or "Great South Gate", in front of the fire-damaged gate in Seoul February 18, 2008. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10 by a 70-year-old arsonist who was angry about a compensation payment. REUTERS/Jo Yong-Hak (SOUTH KOREA)

A woman holding artificial flowers attends a memorial service for the Namdaemun, officially called Sungnyemun or "Great South Gate", in front of the fire-damaged gate in Seoul February 18, 2008. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10 by a 70-year-old arsonist who was angry about a compensation payment. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Labourers work to restore the fire-damaged Namdaemun, officially called Sungnyemun or "Great South Gate", in Seoul February 18, 2008. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10 by a 70-year-old arsonist who was angry about a compensation payment. REUTERS/Jo Yong-Hak (SOUTH KOREA)

Labourers work to restore the fire-damaged Namdaemun, officially called Sungnyemun or "Great South Gate", in Seoul February 18, 2008. The 600-year-old gate, designated as the country's number one national treasure, was burnt down on February 10 by a 70-year-old arsonist who was angry about a compensation payment. REUTERS/Jo Yong-Hak (SOUTH KOREA)

A man works to fence Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008, while an arson suspect reconstructs the events of the arson during an on-the-spot inspection. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

A man leaves a funeral altar set in front of fenced Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008, while an arson suspect reconstructing the events of the arson during on-the-spot inspection. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Policemen stand guard around fenced Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008, while an arson suspect reconstructing the events of the arson during on-the-spot inspection. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Namdaemun (C), officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, is seen in Seoul February 15, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Arson suspect Chae Jong-gi (C) reconstructs the events of the arson during an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. REUTERS/Ahn Hoon/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi (front L) leaves with plainclothes policemen as reporters ask questions after an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. REUTERS/Ahn Hoon/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi (C) leaves with plainclothes policemen as reporters ask questions after an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. REUTERS/Ahn Hoon/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi (C) reconstructs the events of the arson during an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. REUTERS/Ahn Hoon/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi (C) reconstructs the events of the arson during an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Ahn Hoon/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi (2nd L) reconstructs the events of the arson during an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Kwak Sung-ho/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi (3rd L) reconstructs the events of the arson during an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008, as a policeman (R) carries items which Chae used to set the fire. REUTERS/Kwak Sung-ho/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi (L) reconstructs the events of the arson during an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Kwak Sung-ho/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi (2nd L) reconstructs the events of the arson during on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. REUTERS/Ahn Hoon/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi (L) reconstructs the events of the arson during on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. REUTERS/Ahn Hoon/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi reconstructs the events of the arson during on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. REUTERS/Ahn Hoon/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi reconstructs the events of the arson during on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by arson, in Seoul February 15, 2008. REUTERS/Ahn Hoon/Pool (SOUTH KOREA)

Arson suspect Chae Jong-gi leaves in a police van after an on-the-spot inspection with police officers at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire, in Seoul February 15, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Arson suspect Chae Jong-gi (L) leaves in a police van as a policeman blocks photographers after an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire, in Seoul February 15, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Plain-clothes policemen lead arson suspect Chae Jong-gi (front) as they arrive for an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire, in Seoul February 15, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Plain-clothes policemen lead arson suspect Chae Jong-gi (C) as they arrive for an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire, in Seoul February 15, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Plain-clothes policemen lead arson suspect Chae Jong-gi (L) as they arrive for an on-the-spot inspection at Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire, in Seoul February 15, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down a 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

A man wearing a traditional Hanbok plays a traditional flute in front of the fenced gate during a funeral service organised by a civic group for Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire, in Seoul February 12, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Police stand guard at the fenced Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire in Seoul February 12, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire in Seoul is seen February 12, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire in Seoul is seen February 12, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire in Seoul is seen February 12, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

A man bows in front of the fenced gate during a funeral service organised by a civic group for Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire, in Seoul February 12, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Women bow in front of the fenced gate during a funeral service organised by a civic group for Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire in Seoul February 12, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

A man wearing traditional Hanbok plays a traditional flute during a funeral service organised by a civic group for Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire, in front of the fenced gate in Seoul February 12, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

A man wearing a traditional Hanbok plays a traditional flute during a funeral service organised by a civic group for Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire, in front of the fenced gate in Seoul February 12, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)

Namdaemun, officially called Sungnyemun, or "Great South Gate", which was destroyed by fire in Seoul is seen February 12, 2008. South Korean police said on Tuesday they arrested a pensioner who confessed to burning down the 600-year-old gate designated as the country's number one national treasure because he was angry about a compensation payment. REUTERS/Lee Jae-Won (SOUTH KOREA)