The siege of Tripoli occurred in 1551 when the Ottoman Turks and Barbary pirates besieged and vanquished the Knights of Malta in the Red Castle of Tripoli, modern Libya. The Spanish had established an outpost in Tripoli in 1510, and Charles V remitted it to the Knights in 1530. The siege culminated in a six-day bombardment and the surrender of the city on 15 August. The siege of Tripoli was successive to an earlier attack on Malta in July, which was repelled, and the successful invasion of Gozo, in which 5,000 Christian captives were taken and brought on galleys to the location of Tripoli.