The Great Fault is a natural geographical barrier which spans across the whole width of Malta north of Mdina, and practically divides the island in two parts. Its use for defensive purposes can be traced way back to prehistoric times but it was the Knights, in 1722, who were the first to systematically utilize the natural defensive qualities of this geographical feature for military purposes with the building of a number of permanent masonry infantry entrenchments erected along various sections of the position in order to enable the islanders to resist an enemy invasion in the northern part of the island. The militarization of the whole span of the great Fault was a process which was undertaken during the second half of the l9th century by the British military in an attempt to seal off the northern approaches to the fortified Grand Harbour area with its important naval facilities. The North West Front known as the defensive front was initiated in 1875 with the construction of a number of strategically sited forts and batteries designed to stiffen the length of the natural escarpment The fortifications initially consisted solely of three independent, sturdy forts, built in the polygonal style (each with its own separate design) - those at Madliena (Fort Madalena on the eastern extremity of the fortified line), Bingemma (Fort Bingemma, on the Western extremity) and at Mosta (Fort Mosta, commanding the centre). Another central section of the defensive line was fortified by means of a permanent polygonal entrenchment known as the Dwejra Lines. In the 1890s all the fortified strongpoints along the position were linked together with a continuous infantry wall which followed the trace of the natural configuration of the crest of the ridge. Where the line of the fault was interrupted by valleys, the line of fortifications was carried on by means of shallow masonry, fortified bridges, known as stop walls. The defensive qualities of the fortified lines were increased with the addition of a number of batteries, magazines and searchlight emplacements, together with an extensive Barrack complex erected to the rear of the position at Mtarfa. A fourth fortress, Fort Pembroke, was built on the eastern littoral below and to the rear of Fort Madliena. to control the seaward approaches towards Valletta. In 1897, the whole fortified trace, by then nearing completion, was named the Victoria Lines in order to commemorate the Diamond Jubilee of Queen Victoria. At such a late date, however, the defensive position had lost most of its military importance and a military exercise held in May 1900 to test its effectiveness in the event of an enemy invasion revealed that the position could be by-passed with relative ease. By 1907, the Victoria Lines has lost all their military significance and were abandoned altogether. The major forts themselves, with the exception of Fort Mosta, however, continued to play out a dual coastal and defensive role with their heavy 9.2-inch and 6-inch guns.