In 1530, the Maltese islands along with the North African port city of Tripoli were given to the Order of Saint John by Emperor Charles V. The knights settled in the town of Birgu and made it their capital. Soon after their arrival, the Order rebuilt the "Castrum Maris", calling it Fort Saint Angelo. Later on, the entire town of Birgu began to be surrounded by new fortifications, in a similar style to the Order's earlier defences in Rhodes. Birgu's land front was built by 1540. Following the attack of 1551, the Order realised the need to build more defences. Two forts were built in 1552: Fort Saint Elmo at the tip of the Sciberras Peninsula, on the site of an Aragonese watchtower, and Fort Saint Michael on Isola. In 1553, a new fortified city began to be built around Fort Saint Michael, and it was named Senglea after the Grand Master who built it.