Venice had been watching the Peloponnese for decades before the battle. In 1659, the Venetian commander Francesco Morosini had landed briefly at Kalamata during the Cretan War, joined by Maniot and Arvanite fighters, only to sail away without holding it — carrying off the town's own inhabitants to row his galleys. The raid left scars and no gains. When the Ottoman Empire reeled from its catastrophic defeat at Vienna in 1683, Venice seized the moment. In March 1684, it joined the anti-Ottoman Holy League and launched the Morean War, with Morosini — now commander-in-chief — aiming to take the entire Peloponnese as compensation for the recent loss of Crete. His first target was the fortress of Coron, across the Messenian Gulf. After a 49-day siege, Coron fell on 11 August 1685, its Ottoman garrison massacred. Mani rose in revolt. The stage was set for Kalamata.

The army that assembled before Kalamata was one of the more unusual coalitions of the 17th century. The Venetian force numbered around 8,200 when it arrived — 3,100 Venetian mercenaries and Schiavoni troops, 2,400 soldiers from the Duchy of Brunswick-Lüneburg, 1,000 Knights Hospitaller of Malta, 400 Papal troops, and 300 men from Tuscany. Then 3,300 Saxons arrived, bringing the total to over 11,500. Command was placed in the hands of General Hannibal von Degenfeld. Fighting alongside them were Maniot irregulars, mountain warriors from the peninsula south of Kalamata who had been giving up their children as hostages to the Ottomans just months before — and who now wanted revenge. This polyglot Christian force, cobbled together from the courts and mercenary markets of Western Europe and the mountain clans of the southern Peloponnese, faced an Ottoman army defending a fortified camp on ground they had chosen.

The battle began at dawn on 14 September. Both sides advanced. On the Venetian right, Ottoman sipahi cavalry moved into the hills to outflank the Hanoverians — but the heights were already held by Maniot fighters, who had moved there first. On the left, Saxon troops repulsed the cavalry. Along the entire front, the Venetians pushed forward, pressing the Ottomans back through the streets of the town. As the retreat became a rout, the Ottomans set fire to their own supply and ammunition stores. The explosions shook the castle above the town. Venetian commanders climbed a nearby hill to watch the fires confirm what the battle had already decided. Kalamata had fallen.

Victory brought an act of deliberate destruction. The Ottoman ammunition blasts had already damaged Kalamata Castle badly; the Venetians, examining what remained, judged the hilltop fortification obsolete — an artifact of an earlier age of warfare that predated the artillery that had now made such walls irrelevant. They demolished what stood. Guns were removed. The houses inside the castle walls were burned. The gates and bastions were blown up. The fortress that had anchored the town for centuries, that the Villehardouin princes had called home, that Slavic raiders had scaled with a rope-measured ladder in the 1290s, was razed by the people who had just conquered it. The Venetians would later rebuild the outer circuit wall — the Lion of Saint Mark still marks the main gate — but the castle never recovered its former role. The battle of September 1685 broke both an army and a citadel.