Hospitaller Malta, known in Maltese history as the Knights' Period, was a de facto state which existed between 1530 and 1806 when the Mediterranean islands of Malta and Gozo were ruled by the Order of St. John of Jerusalem. It was formally a vassal state of the Kingdom of Sicily, and it came into being when Emperor Charles V granted the islands as well as the city of Tripoli in modern Libya to the Order, following the latter's loss of Rhodes in 1522. Later in 1548 Charles V elevated the town Order controlled town of Heitersheim of the Holy Roman Empire, to the status of a principality, granting the Order formal control of the fief. Hospitaller Tripoli was lost to the Ottoman Empire in 1551, but an Ottoman attempt to take Malta in 1565 failed.