In the Northern part of the Greek Peninsula Peloponnese (nom Achaia) at the foot of mount Panachaiko lie the ruins of the castle of Salonika (also known as castle of Orgia or Oria).

Castle of Salonika was built by the Achaean barons of the Principality about 1280-1310 years. The castle was built on top of the picturesque steep hill, near which flowed the river Fontas. It was the perfect place for a fortress. Soon the walls of the castle rose the big city.

In 1460 the troops of the Sultan of the Ottoman Empire Mehmed II invaded the Peloponnese and the city of the despotate of Morea (the land of the Peloponnese came under the control of the Byzantine Empire and Principality of Achaia's and ceased to exist altogether) one after another, almost without offering resistance, under the control of the Turks. Salonika under the leadership of Gritsai Paleologus held siege for almost a year and only when the Janissaries was blocked by water, the city capitulated. About 6,000 residents of Salonika were enslaved, and 900 boys aged 7 to 14 years were selected for Devshirme ("blood tribute", "tax in blood" – a system of forced recruitment of boys their Christian families with subsequent conversion to Islam and education for the service of the sublime Porte).

Meanwhile, the castle continued to hold the Fort. Gretsas and his supporters, who was still in the citadel, agreed to surrender, but laid down the conditions under which they should be able to leave the fortress. Mehmed II has accepted the terms and went in Egio, leaving his place as Governor of the Peloponnese and Vesalii Homosassa who ignored the Treaty and ordered his men to grab the first man who tries to leave the castle. Learning of this, Mehmed II replaced Homosassa Zaganos Pasha and left the Peloponnese. Zaganos Pasha has also resumed the siege of the castle, but, nevertheless, Gretsas Paleologos still managed to escape and get to the coast, whence he went to the Venetian fortress of Lepanto (modern Naupactus), where he found refuge.

The fall in Salonika marked the complete submission of the Peloponnesian lands (except Venetian Nafplio, Methoni and koroni) of the Ottoman Empire.

Unfortunately, to the present day from the city of Salonika and the majestic castle remained only ruins. Relatively well preserved only medieval bridge.