The treaty which Venice signed with the Sultan Mehmed in November 1419 listed by name all the towns and islands in Romania which the Sultan recognised as being Venetian possessions. There were thirtyeight. The number had grown in accordance with their policy of establishing a solid line of defence west and south of Tenedos and the straits. The Turks might take Constantinople, but they would have to concede that the Aegean islands and the harbours of the Morea and Greece belonged to Venice. In the years before 1419 the valuable Greek ports of Navarino, Clarentza, Patras and Lepanto (Naupaktos) had more or less voluntarily accepted Venetian rule. On the other hand, the expansion and prosperity of the Byzantine Despotate of the Morea was not always to the liking of Venice. The Senate had applauded the construction of the Hexamilion wall across the Isthmus of Corinth in 1415 but they had declined to contribute to its cost. They had ferried the Emperor Manuel back to Constantinople and brought his son John out to join his brother, the Despot Theodore II. In the Despot's incessant warfare against the last of the Latin Princes of Achaia, however, the Venetians tried to remain neutral; and they had to lodge numerous complaints about the damage being done to their property and their citizens.

The new Ottoman Sultan Murad II began his siege of Constantinople towards the end of June 1422. It was the worst that the Byzantines had endured. The Sultan did everything that he could to break their resistance.