The Cottonera Lines,

The largest works of fortifications built by the Knights of Malta, work started in 1670 by Antonio Maurizo Valperga and were paid for in the most part by Grand Master Nicolas Cotoner.
It was much criicised by other engineers of the day, work moved on a pace with the fall of Candia (Crete) to the Turks for fear of another seige on Malta.
It is a long semi circle of Curtain wall 4.5K long with 8 Bastions and 2 Semi Bastions, it was to have 8 revelins (some times called Demi-Lunes) but the money ran out,powder magazines were built into some of the Bastions and mid way through some of the walls were 5 gate ways, (some now bricked up) the best of these is the Baroque Gate known as the Zabbar Gate with a bust of Grand Master Contoner.
In 1714 engineer de-Tigne reported that the lines still needed a large amount of money to finish them off, with the Order short of money in 1720 he began to build a retrenchment around the most northerly Bastion and turned it into Fort Salvalore.
When the British arrived in 1800 they strenthened the lines by building a joining entrenchment between the back of the lines to the Margarita forming Fort Firenzuola, the British armed the walls with 10" guns .
The lines were never tested in a seige other than when the Maltses held the French with in its walls for 2 years between 1798-1800.