Sidon's Sea Castle (Arabic: قلعة صيدا البحرية, romanized: Kalaat Saida al-Bahriya) was built by the crusaders in the thirteenth century as a fortress of the Holy Land.

In AD 1228, the Crusaders built Sidon's Sea Castle as a fortress on a small island connected to the mainland by a narrow 80m long roadway.

It was partially destroyed by the Mamluks when they took over the city from the Crusaders, but they subsequently rebuilt it and added the long causeway.

The castle later fell into disuse, but was again restored in the 17th century by Emir Fakhreddine II, only to suffer great damage.

There has also been evidence of the old Phoenician city being buried under the sea in the area surrounding the castle: structures of walls, columns, stairways, remains of buildings, statues and cisterns.