On October 31st 1448 Emperor John VIII died without an heir. His brother Constantine, who was then despot of Mystra, ascended the throne. Legend has it that he was crowned emperor in the capital of the despotate, in January 1449, but we can be sure that two months later he travelled to Constantinople, where he was given a triumphant welcome. Constantine rose to the throne at an absolutely critical time for the empire. Thessaloniki, the second largest city in Byzantium, had already been under Ottoman rule for twenty years, after falling to forces under Murad II, while the greater part of Macedonia was in Turkish hands by the late 14th century. The only free state in the southern Balkans was the Despotate of Mystras.

As a despot Constantine had showed great skill. By 1444 he had succeeded in rebuilding the Examilion Wall at Corinth and in recapturing Athens and Thebes. The following year his forces marched into Central Greece and he himself reached Mount Pindos, where Albanian and Vlach populations joined forces with him. He made several attempts to curb the power of the Venetians, who held Argos and Nafplion on the east coast of the Peloponnese, and Koroni and Methoni on the west. However, in November 1446 Murad II’s cannons destroyed Examilion and his troops devastated the northern Peloponnese as far as Killini. Constantine and his brother Thomas managed to escape with a handful of their troops, while the Turks withdrew not long afterwards.

After the fall of Constantinople the Ottomans experienced great difficulty in advancing into the Peloponnese. It was only in 1460 that Demetrius Palaeologus was forced to surrender Mystras, and other cities put up fierce resistance. The residents of Monemvasia sought the protection of Pope Pius the Second, finally surrendering the city to the Venetians late in 1463. Since they did not wish to engage in war with Venice, the Ottomans did not launch attacks against Methoni and Koroni, which only fell into their hands in 1500, followed by Nafplion forty years later.