This old castle, São Jorge, is likely one of the oldest, historical sites to visit in Lisbon. The hill that Saint George Castle is situated on, was previously inhabited by the Celtic tribe, the Phoenicians, Greeks, Carthaginians and Romans. This site was built in the 10th century as a protection against invading groups; the first walls were built in order to do this. Centuries later, the castle survived through many earthquakes, sieges and even the ever-changing rulers.