The Saints Peter and Paul Counter-guard is an integral part of Valletta's original historic fortifications, constructed between 1630-1640 in response to the imminent threat of a Turkish invasion. Its construction was proposed by the Hospitaller Knight Don Giovanni de Medici, Marquis of St. Angelo. He advocated for the erection of a series of four counter-guards beyond the Valletta ditch to shield its land-front from long-range bombardment, given the advancing capabilities of artillery in the 17th century.

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In 1940, it became part of the new Combined War Headquarters (War HQ Tunnels) established beneath the Upper Barracca Gardens by the British armed forces. Several radio communication masts were installed on it to serve the War HQ. In 1941, excavation commenced beneath it to create the St. Peter Galleries, intended to house the operational side of the new War HQ.

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This counterguard stands as the best-preserved one and the only one in Valletta still standing in its original form., it retains nearly all of its original features, including its stone échauguette—the overhanging, wall-mounted turret designed for enemy sighting. The counter-guard encompasses a sizable 19th-century Gun Powder Magazine, which once supplied a significant portion of the artillery on the city walls, as well as a complete WW2 Mine-watching Post, intact 17th-century artillery steps, musketry platforms, two British 19th-century 24-pr carronades on their reclining platforms, various gates, and a stone fly bridge connecting it to the city's land front. Additionally, it is home to the oldest tree in Valletta, dating back to the Republican French occupation of Malta, making it approximately 200 years old. Plans are underway to restore its portcullis gate and drawbridge in the near future.