A boy sits in a window of a watchtower while visiting the Mutianyu section of the Great Wall of China on the first day of the five-day Labour Day holiday following the coronavirus disease (COVID-19) outbreak, on the outskirts of Beijing, China May 1, 2020. REUTERS/Thomas Peter

Tourists walk inside a watchtower while visiting the Mutianyu section of the Great Wall of China on the first day of the five-day Labour Day holiday following the coronavirus disease (COVID-19) outbreak, on the outskirts of Beijing, China May 1, 2020. REUTERS/Thomas Peter TPX IMAGES OF THE DAY

Tourists walk inside a watchtower while visiting the Mutianyu section of the Great Wall of China on the first day of the five-day Labour Day holiday following the coronavirus disease (COVID-19) outbreak, on the outskirts of Beijing, China May 1, 2020. REUTERS/Thomas Peter

An Israeli watchtower is seen as Palestinians stand at the Israel-Gaza border fence in the southern Gaza Strip, February 28, 2020. Picture taken February 28, 2020. REUTERS/Ibraheem Abu Mustafa

A watchtower is seen near Greece's border crossing with Turkey in Kastanies, Greece March 5, 2020. REUTERS/Florion Goga

A watchtower is seen near Greece's border crossing with Turkey in Kastanies, Greece March 5, 2020. REUTERS/Florion Goga

An anti-U.S. President Donald Trump mural is seen on a section of the Israeli barrier and a watchtower in Bethlehem in the Israeli-occupied West Bank January 29, 2020. REUTERS/Mussa Qawasma

An anti-U.S. President Donald Trump mural is seen on a section of the Israeli barrier and a watchtower in Bethlehem in the Israeli-occupied West Bank January 29, 2020. REUTERS/Mussa Qawasma

The watchtowers of former Nazi German Auschwitz-Birkenau concentration camp complex are pictured in Oswiecim, Poland, January 14, 2020. Picture taken January 14, 2020. REUTERS/Axel Schmidt

A watchtower is photographed at the fenced area which will be used as heliport during the upcoming World Economic Forum (WEF) in Davos, Switzerland January 13, 2020. REUTERS/Arnd Wiegmann

A watchtower is photographed at the fenced area which will be used as heliport during the upcoming World Economic Forum (WEF) in Davos, Switzerland January 13, 2020. REUTERS/Arnd Wiegmann

A watchtower is photographed at the fenced area which will be used as heliport during the upcoming World Economic Forum (WEF) in Davos, Switzerland Januar 13, 2020. REUTERS/Arnd Wiegmann

A U.S. Army soldier is seen at a watchtower of the U.S. Embassy during a protest to condemn air strikes on bases belonging to Hashd al-Shaabi (paramilitary forces), in Baghdad, Iraq January 1, 2020. REUTERS/Khalid al-Mousily

A Palestinian flag flutters near an Israeli watchtower in Bethlehem, in the Israeli-occupied West Bank December 2, 2019. Picture taken December 2, 2019. REUTERS/Mussa Qawasma

The silhouette of a former watchtower is seen during an event marking the 30th anniversary of the fall of the Berlin Wall at a former border crossing between Eastern and Western Germany in the former border village of Moedlareuth, Germany November 9, 2019. REUTERS/David W Cerny

German Foreign Minister Heiko Maas and U.S. Secretary of State Mike Pompeo walk past a former border watchtower at a memorial site during their visit to the village of Moedlareuth near Hof, Germany November 7, 2019. John Macdougall/Pool via REUTERS

German Foreign Minister Heiko Maas and U.S. Secretary of State Mike Pompeo pose near a former border watchtower during their visit to the village of Moedlareuth near Hof, Germany November 7, 2019. John Macdougall/Pool via REUTERS

German Foreign Minister Heiko Maas speaks to U.S. Secretary of State Mike Pompeo joined by U.S. Ambassador to Germany Richard Grenell near a former border watchtower during their visit to the village of Moedlareuth near Hof, Germany November 7, 2019. John Macdougall/Pool via REUTERS

A sign reading "Security corridor - trespassing prohibited" stands in front of a fence and a watchtower on the compound of the German-German Museum ("Deutsch-Deutsches Museum") in Moedlareuth, Germany, October 3, 2019. REUTERS/Andreas Gebert

A sign reading "Security corridor - trespassing prohibited" stands in front of a fence and a watchtower on the compound of the German-German Museum ("Deutsch-Deutsches Museum") in Moedlareuth, Germany, October 3, 2019. REUTERS/Andreas Gebert

Yellow flowers grow in a field in front of a former watchtower near the German-German Museum ("Deutsch-Deutsches Museum") in Moedlareuth, Germany, October 3, 2019. REUTERS/Andreas Gebert

Yellow flowers grow in a field in front of a former watchtower near the German-German Museum ("Deutsch-Deutsches Museum") in Moedlareuth, Germany, October 3, 2019. REUTERS/Andreas Gebert

Visitors walk past a former watchtower on the compound of the German-German Museum ("Deutsch-Deutsches Museum") in Moedlareuth, Germany, October 3, 2019. REUTERS/Andreas Gebert

A police officer and another man stand in front of a former watchtower on the compound of the German-German Museum ("Deutsch-Deutsches Museum") in Moedlareuth, Germany, October 3, 2019. REUTERS/Andreas Gebert

A French soldier stands guard in a watchtower at the Relay Desert Platform Camp (PfDR) during Operation Barkhane in Gossi, Mali, July 30, 2019. Picture taken July 30, 2019. REUTERS/Benoit Tessier

A French military watchtower is pictured at the Relay Desert Platform Camp (PfDR) during Operation Barkhane in Gossi, Mali, July 30, 2019. Picture taken July 30, 2019. REUTERS/Benoit Tessier

People stand on a watchtower at the end of a jetty in the Mediterranean Sea as Tel Aviv's skyline of high-rise buildings is seen in the background, in Jaffa, Israel June 16, 2019. Picture taken June 16, 2019. REUTERS/Amir Cohen

A kitchen is pictured in a watchtower at a training camp allegedly linked to Islamist militants, in Kattankudy near Batticaloa, Sri Lanka, May 5, 2019. REUTERS/Danish Siddiqui

Police officers stand outside a room in a watchtower at a training camp allegedly linked to Islamist militants, in Kattankudy near Batticaloa, Sri Lanka, May 5, 2019. REUTERS/Danish Siddiqui

A watchtower is seen at a training camp allegedly linked to Islamist militants in Kattankudy, near Batticaloa, Sri Lanka, May 5, 2019. REUTERS/Danish Siddiqui

View of a watchtower at the prison where an inmate in one of France's most secure prisons stabbed two guards with a knife in Conde-sur-Sarthe, France, March 5, 2019. REUTERS/Benoit Tessier

View of a watchtower at the prison where an inmate in one of France's most secure prisons stabbed two guards with a knife in Conde-sur-Sarthe, France, March 5, 2019. REUTERS/Benoit Tessier

A Pakistani soldier ties his national flag upside down on a watchtower as seen across the fenced border between India and Pakistan in Ranbir Singh Pura sector near Jammu March 1, 2019. REUTERS/Adnan Abidi

A bird flies near a Pakistani watchtower across the fenced border between India and Pakistan in Ranbir Singh Pura sector near Jammu March 1, 2019. REUTERS/Adnan Abidi

An Indian Border Security Force (BSF) bunker (C) and a Pakistani watchtower (L) are pictured near the fenced border with Pakistan in Ranbir Singh Pura sector near Jammu March 1, 2019. REUTERS/Adnan Abidi

A woman dumps garbage as a Pakistani watchtower is seen behind the fenced border between India and Pakistan, at a village in Ranbir Singh Pura sector near Jammu March 1, 2019. REUTERS/Adnan Abidi

A woman carries garbage to dump as a Pakistani watchtower is seen behind the fenced border between India and Pakistan, at a village in Ranbir Singh Pura sector near Jammu March 1, 2019. REUTERS/Adnan Abidi

Swiss soldiers stand on a watchtower at an area which will be used as heliport during the upcoming World Economic Forum (WEF) in Davos, Switzerland January 15, 2019. REUTERS/Arnd Wiegmann

A watchtower stands at the fenced ares which will be used as heliport during the upcoming World Economic Forum (WEF) in Davos, Switzerland Januar 12, 2019. REUTERS/Arnd Wiegmann

Policemen look out from a watchtower at the Chilean and Peruvian border, near Arica, Chile, November 16, 2018. REUTERS/Ivan Alvarado SEARCH "ALVARADO ARICA" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES.

An Israeli watchtower is seen as Palestinian demonstrators gather during a protest at the Israel-Gaza border fence, in the southern Gaza Strip December 14, 2018. REUTERS/Ibraheem Abu Mustafa

A guard watchtower rises along a perimeter fence of what is officially known as a vocational skills education centre in Dabancheng in Xinjiang Uighur Autonomous Region, China September 4, 2018. This centre, situated between regional capital Urumqi and tourist spot Turpan, is among the largest known ones, and was still undergoing extensive construction and expansion at the time the photo was taken. Picture taken September 4, 2018. To match Special Report MUSLIMS-CAMPS/CHINA REUTERS/Thomas Peter TPX IMAGES OF THE DAY

An Egyptian watch tower is seen from the Israeli side of the Israel-Egypt border in southern Israel September 26, 2018. Picture taken September 26, 2018 REUTERS/ Amir Cohen

A watch tower for wood fires is seen in this aerial view, during a long-lasting heatwave over central Europe near Haltern, Germany, August 4, 2018. REUTERS/Wolfgang Rattay

Two Greek Army watchtowers (L) and one Turkish Army watchtower are seen at the borderline between Greece and Turkey, near the village of Nea Vyssa, Greece, April 30, 2018. REUTERS/Alkis Konstantinidis SEARCH "EVROS MIGRANTS" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES.

A general view of Damascus during sand storm and heavy rain, Syria April 26, 2018. REUTERS/Omar Sanadik

Chinese men fish as watchtowers are seen on the North Korean side of the Yalu River just north of Dandong, in China's Liaoning Province, November 20, 2017. REUTERS/Damir Sagolj

Chinese men fish as a watchtower stands on the North Korean side of the Yalu River, just north of Dandong in Liaoning province, China, November 20, 2017. In the Chinese city of Dandong, signs of neighbouring North Korea are pervasive. REUTERS/Damir Sagolj SEARCH "SAGOLJ ROAD TRIP" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES.

A North Korean watchtower is photographed from the Chinese side of the Yalu River east of Linjiang, China, November 22, 2017. A week-long road trip along China's side of its border with North Korea showed places where it is porous. REUTERS/Damir Sagolj SEARCH "SAGOLJ ROAD TRIP" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. TPX IMAGES OF THE DAY

Chinese men fish as a watchtower stands on the North Korean side of the Yalu River, just north of Dandong in Liaoning province, China, November 20, 2017. In the Chinese city of Dandong, signs of neighbouring North Korea are pervasive. REUTERS/Damir Sagolj SEARCH "SAGOLJ ROAD TRIP" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES.

A North Korean watchtower is photographed from the Chinese side of the Yalu River east of Linjiang, China, November 22, 2017. A week-long road trip along China's side of its border with North Korea showed places where it is porous. REUTERS/Damir Sagolj SEARCH "SAGOLJ ROAD TRIP" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. TPX IMAGES OF THE DAY

Tourists walk near Dwejra Tower, a watchtower built in 1652, outside the village of San Lawrenz on the island of Gozo, Malta, January 25, 2018. REUTERS/Darrin Zammit Lupi

Tourists walk up to Dwejra Tower, a watchtower built in 1652, outside the village of San Lawrenz on the island of Gozo, Malta, January 25, 2018. REUTERS/Darrin Zammit Lupi

View of Nantes' jail in Carquefou near Nantes as prison wardens attend a nationwide protest, France, January 15, 2018. REUTERS/Stephane Mahe

A watchtower is seen at "La Rolandiere" area in the zoned ZAD (Deferred Development Zone) in Notre-Dame-des-Landes, that is slated for the Grand Ouest Airport (AGO), western France January 9, 2018. Picture taken January 9, 2018. REUTERS/Stephane Mahe

A watchtower is seen at "La Rolandiere" area in the zoned ZAD (Deferred Development Zone) in Notre-Dame-des-Landes, that is slated for the Grand Ouest Airport (AGO), western France January 9, 2018. Picture taken January 9, 2018. REUTERS/Stephane Mahe

Members of Palestinian security forces loyal to Hamas stand guard as an Israeli watchtower is seen in the background, in Khan Younis in the southern Gaza Strip November 3, 2017. REUTERS/Ibraheem Abu Mustafa

A French soldier uses his binoculars from a watchtower at the Relay Desert Platform Camp (PfDR) in Ansongo, Mali, October 15, 2017, during the regional anti-insurgent Operation Barkhane. Picture taken October 15, 2017. REUTERS/Benoit Tessier

General view of a watchtower at the Relay Desert Platform Camp (PfDR) in Ansongo, Mali, October 15, 2017, during the regional anti-insurgent Operation Barkhane. Picture taken October 15, 2017. REUTERS/Benoit Tessier

Prison guards stand in a watchtower at the Najayo prison where suspects in a bribery scandal engulfing Brazilian company Odebrecht, were transferred on Monday,in Najayo, Dominican Republic June 12, 2017. REUTERS/ Ricardo Rojas