St. George's Castle is one of the oldest buildings in Lisbon and one of the most important attractions. The castle is built at the highest point in the Alfama area, and there is still a community called Holy Cross in the castle. There were traces of human inhabitation here as early as the 6th century BC, and many peoples such as the Phoenicians, Greeks, and Carthage left footprints here. The castle has a long history, built by the Celtic in the 5th century, and later the Moors and Christians were reinforced on the original basis, and was once transformed into a palace. It covers an area of 6,000 square meters and was once an important strategic commanding height, which was occupied by rulers of various eras. The moving story of the crusaders who attacked the castle has been circulated to this day. It is legendary that Matias Monis saw the city gate with only a small mouth, and used his own body to stop the city gate from closing, so that the army successfully entered the castle and drove away the Moors.