Fort Bassein, also known as the Vasai Fort or Fort Baçaim , is a large fort in the town of Vasai in the Palghar district of Maharashtra state in the Konkan division in India.
The complete form of the Portuguese name is "Fortaleza de São Sebastião de Baçaím" or the Fort of St. Sebastian of Vasai.
The fort had been under the influence of 4 kingdoms. In the early 1500's it was under the control of Sultan Bahadur of Gujarat. The Treaty of Bassein (1534) was signed by Sultan Bahadur of Gujarat and the Kingdom of Portugal. After this it was under the control of Portuguese dynasty.