On the West Coast of the Thermaic Gulf, one kilometer to the south of Makrigialos you can find the ruins of the Byzantine Castle of the Bishop of Kitros. These ruins, together with the western gate of the Castle (opposite the Church), the foundations of an inn, baths and a small single chamber temple were uncovered during the period 1983 - 1992 whilst the site was being excavated by the Society of Byzantine Antiquities of Thessaloniki. These are the only visible remains left today of Byzantine Pydna, which was renamed Kitros in the 6th or 7th and century and was, until the 14th century, the most important city in medieval Pieria.

Inside the Castle two old Christian Basilicas dating from the 4th and 6th century are located, the last of which was destroyed in the Bulgarian occupation of the fortress, an event which took place from 913 - 924. At the end of the 10th century a large scale Church was built with a dome and cloister, 23.20 m. by 16.60 m., decorated with mosaics, wall paintings and some remarkable sculptures, and this must have been the Cathedral Church of Kitros.

Kitros was the seat of the local administrator (an administrative sub-division of the Byzantine Empire) answerable to the regional administration in Veria, and during the 11th and 12th century was the center of production for tiles and also a busy trading port. Evidence for this has been provided by the uncovering of a ceramic factory complete with furnace and a 12th century inn, along with its baths, in the port area. Pydna's commanding position came to an end with the arrival of the Franks in 1204, as can be seen from the objects unearthed from in front of the Castle showing the effects of the siege and the burning and plundering of the entire habitation.

After the burning of the Cathedral the community built two small single room shrines in the area near the port, next to the inn. Outside and roundabout the area a cemetery containing graves and tombs with tiled roofs have been dug up. In 1343, during the civil war between Ioannis Palaeologos and the claimant to the throne, Ioannis Kantakouzinos, the castle was besieged and captured by the soldiers of the rightful Emperor Ioannis Apokafko, and in the autumn of the same year by the Turkish Admiral, Amour.
At the end of the 15th century the site was abandoned because of continual attacks by pirates, and the inhabitants moved to the site of present day Kitros.