The Battle of Diu sometimes referred as the Second Battle of Chaul was a naval battle fought on 3 February 1509 in the Arabian Sea, near the port of Diu, India, between the Portuguese Empire and a joint fleet of the Sultan of Gujarat, the Mamlûk Burji Sultanate of Egypt, the Zamorin of Calicut with support of Ottomans, the Republic of Venice and the Republic of Ragusa (Dubrovnik).
The Portuguese victory was critical: Mamluks and Arabs retreated, easing the Portuguese strategy of controlling the Indian Ocean to route trade down the Cape of Good Hope, circumventing the traditional spice route controlled by the Arabs and the Venetians through the Red Sea and Persian Gulf. After the battle, Portugal rapidly captured key ports in the Indian Ocean like Goa, Ceylon, Malacca and Ormuz, crippling the Mamluk Sultanate of Egypt and the Gujarat Sultanate, greatly assisting the growth of the Portuguese Empire and setting its trade dominance for almost a century, until it was taken during the Dutch-Portuguese War and the Battle of Swally won by the British East India Company in 1612. It marks the beginning of the European colonialism in Asia. It also marks the spillover of the Christian-Islamic power struggle, in and around the Mediterranean Sea and the Middle East, into the Indian Ocean which was the most important region for international trade at the time.