In 1535 Bahadur Shah, the Sultan of Gujarat, concluded a defensive alliance with the Portuguese against the Mughal emperor Humayun, and allowed the Portuguese to construct the Diu Fort and maintain a garrison on the island. The alliance quickly unraveled, and attempts by the Sultans to oust the Portuguese from Diu between 1537 and 1546 failed. The Siege of Diu by the Ottoman Empire in 1538 was unsuccessful at repelling the Portuguese. The fortress, completed by Dom João de Castro after the siege of 1545, still stands. The island was occupied by the Indian military on 19 December 1961.
Diu was a city of great commercial activity when the Portuguese arrived in India. In 1513, the Portuguese tried to establish an outpost there, but negotiations were unsuccessful. In 1531 the conquest attempted by D. Nuno da Cunha was also not successful. However, Diu was offered to the Portuguese in 1535 as a reward for military aid they gave to the Sultan Bahadur Shah of Gujarat, against the Great Mogul of Delhi. So coveted since the times of Tristão da Cunha and Albuquerque, and after failed attempts of Diogo Lopes de Sequeira in 1521, Nuno da Cunha in 1523, Diu was offered to the Portuguese, who soon fortified it.
Having repented of his generosity, Bahadur Shah sought to recover Diu, but was defeated and killed by the Portuguese, followed by a period of war between them and the people of Gujarat. In 1538, Coja Sofar, lord of Cambay, together with the Turkish Suleiman Pasha, came to lay siege to Diu, and were defeated by Portuguese resistance led by Anthony Silveira. A second siege was imposed by the same Coja Sofar, in 1546, and repelled by the Portuguese conquerors, led on land by D. John Mascarenhas, and at sea, by D. João de Castro. Coja Sofar and D. Fernando de Castro, son of the Portuguese viceroy, perished in the struggle.
After this second siege, Diu was so fortified that it could withstand later attacks of the Arabs of Muscat and the Dutch (in the
