Mexican President Vicente Fox (L), U.S. President George Bush (C) and Canadian Prime Minister Stephen Harper climb the Castle, or Kukulkan Pyramid, as they tour the Mayan ruins of Chichen Itza in Mexico's Yucatan peninsula March 30, 2006. The three leaders began their meetings in Cancun to discuss immigration, border security and trade with a visit to the Chichen Itza ruins. REUTERS/Chris Wattie