All contemporary sources indicate the Turks intended to proceed to the Tunisian fortress of La Goletta and wrest it from the Spaniards, and Suleiman had also spoken of invading Europe through Italy.
However, modern scholars tend to disagree with this interpretation of the siege’s importance. H.J.A. Sire, a historian who has written a history of the Order, is of the opinion that the siege represented an overextension of Ottoman forces, and argues that if the island had fallen, it would have quickly been retaken by a massive Spanish counterattack.
Although Don Garcia did not at once send the promised relief (troops were still being levied), he was persuaded to release an advance force of some 600 men. After several attempts, this piccolo soccorso (Italian: small relief) managed to land on Malta in early July and sneak into Birgu, raising the spirits of the besieged garrison immensely.
On 15 July, Mustafa ordered a double attack against the Senglea peninsula. He had transported 100 small vessels across Mt. Sciberras to the Grand Harbour, thus avoiding the strong cannons of Fort St. Angelo, in order to launch a sea attack against the promontory using about 1,000 Janissaries, while the Corsairs attacked Fort St. Michael on the landward end. Luckily for the Maltese, a defector warned de Valette about the impending strategy and the Grand Master had time to construct a palisade along the Senglea promontory, which successfully helped to deflect the attack. Nevertheless, the assault probably would have succeeded had not the Turkish boats come into point-blank range (less than 200 yards) of a sea-level battery of five cannons that had been constructed by Commander Chevalier de Guiral at the base of Fort St. Angelo with the sole purpose of stopping such an amphibious attack. Just two salvos sank all but one of the vessels, killing or drowning over 800 of the attackers. The land attack failed simultaneously when relief forces were able to cross to Ft. St. Michael across a floating bridge, with the result that Malta was saved for the day.
The Turks by now had ringed Birgu and Senglea with some 65 siege guns and subjected the town to what was probably the most sustained bombardment in history up to that time. (Balbi claims that 130,000 cannonballs were fired during the course of the siege.) Having largely destroyed one of the town’s crucial bastions, Mustafa ordered another massive double assault on 7 August, this time against Fort St. Michael and Birgu itself. On this occasion, the Turks breached the town walls and it seemed that the siege was over, but unexpectedly the invaders retreated. As it happened, the cavalry commander Captain Vincenzo Anastagi, on his daily sortie from Mdina, had attacked the unprotected Turkish field hospital, massacring the sick and wounded. The Turks, thinking the Christian relief had arrived from Sicily, broke off their assault.
After the attack of 7 August, the Turks resumed their bombardment of St. Michael and Birgu, mounting at least one other major assault against the town on 19–21 August. What actually happened during those days of intense fighting is not entirely clear.
Bradford’s account of the climax of the siege has a mine exploding with a huge blast, breaching the town walls and causing stone and dust to fall into the ditch, with the Turks charging even as the debris was still falling. He also has the 70-year-old de Valette saving the day by leading towards the Turks some hundred troops that had been waiting in the Piazza of Birgu. Balbi, in his diary entry for 20 August, says only that de Valette was told the Turks were within the walls; the Grand Master ran to “the threatened post where his presence worked wonders. Sword in hand, he remained at the most dangerous place until the Turks retired.” Bosio also has no mention of the successful detonation of a mine. Rather, in his report a panic ensued when the townspeople spied the Turkish standards outside the walls. The Grand Master ran there, but found no Turks. In the meantime, a cannonade atop Ft. St. Angelo, stricken by the same panic, killed a number of townsfolk with friendly fire
On 7 September, Don Garcia had at last landed about 8,000 men at St. Paul’s Bay on the north end of the island. The so-called Grande Soccorso (“great relief”) positioned themselves on the ridge of San Pawl tat-Tarġa, waiting for the retreating Turks. It is said that when some hot-headed knights of the relief force saw the Turkish retreat and the burning villages in its wake, they charged without waiting for orders from Ascanio della Corgna. Della Corgna had no choice but to order a general charge which resulted in the massacre of the retreating Turkish force. The Turks fled to their ships and from the islands on 11 September. Malta had survived the Turkish assault, and throughout Europe people celebrated what would turn out to be the last epic battle involving Crusader Knights.
The number of casualties is in as much dispute as the number of invaders. Balbi gives 35,000 Ottoman deaths, which seems implausible, while Bosio estimates 30,000 casualties, including sailors. Modern estimations from military historians using Turkish archives have put the number of casualties at 10,000 from combat and disease, though it is generally agreed that there were likely far more losses amongst the various volunteers and pirates, which the Turkish sources would not have noted. The knights lost a third of their number, and Malta lost a third of its inhabitants. Birgu and Senglea were essentially leveled. Still, 9,000 defenders had managed to withstand a siege of more than four months in the hot summer, despite enduring a bombardment of some 130,000 cannonballs.