San Juan was founded in 1521. It was named after San Juan Bautista, or St. John the Baptist (name given by Christopher Columbus). San Juan is also known as "La Ciudad Amurallada". This means the "walled city". San Juan has many old buildings still standing today. Many Spanish explorers came during the Age of Discovery and built forts, churches, and other historical buildings. An example of a very old fort is "La Fortaleza". It is also known as "Palacio de Santa Catalina". In the sixteenth century, it was a Spanish fortress against Caribs. These were the people native to the Caribbean islands and Central America. Another old building is the oldest residence in Old San Juan, Casas de los Contrasfuertes (House of Buttresses).