The castle of Pydna (Kitros) is situated on the west coast of the Thermaic Gulf, near the village of Makrygialos in Pieria. It was founded in the 6th century by Justinian I at the site of ancient Pydna?s citadel. The new castle was rectangular, with dimensions of 320m x 130m, and occupied an area of 50 acres. It acquired a new name, Kitros, like many other castles that were founded on the sites of ancient cities. A large gate at the western enclosure, protected on the right and left by two rectangular towers, was the castle?s main entrance.

The most important building inside the castle was the bishopric?s basilica, built at the end of the 6th century, which was directly adjacent to the eastern wall. An anonymous military text from the 10th century informs us of the capture of Kitros by the Bulgarians, which resulted in the razing of the bishopric?s basilica and the capture of the bishop. Following this successful raid on the castle, the arches of the castle?s internal wall were built, and a second wall was constructed outside the original wall. It was then when the contemporary preserved church was built, around the end of the 10th century/start of 11th century, the architectural form of which was a small-scale imitation of the Church of Agia Sophia in Thessaloniki.

Due to its port and salt evaporation ponds, Kitros emerged as the most important city in Pieria during the Byzantine era and its bishopric was ordered first out of the ten such bishoprics that were subject to the metropolitan bishop of Thessaloniki during the 10th century. The city reached its peak during the 12th century when it was the seat of a ?katepanikia? (an administrative division of the empire). The castle was conquered in 1204, after a siege by the Franks of Boniface I, Marquess of Montferrat, who burned down the entire settlement and turned the burned bishopric church into military camps. They raised the three-storey tower of their Despot, Wirich von Daum, upon the site of the sanctuary. After the departure of the Franks, the castle and city were still among the most prominent cities in Pieria. In 1343, during the second Byzantine civil war, Kitros acceded to Kantakouzinos, but during the summer of the same year it was besieged and conquered by a supporter of John Palaiologos, Grand Duke Apokafkos. In 1345 the castle was occupied by the Serbs and was given as a fief to the Serbian despot Thomas Preliubovic. After the middle of the 15th century, a family had settled in the ruins of the military camp, signifying the destruction and abandonment of the castle, which had been taken over by the Ottomans in 1386.