By the spring of 1825, Ibrahim Pasha's Egyptian expeditionary force had overrun much of the western Peloponnese. Ibrahim commanded both a powerful army — Western-trained, equipped with modern artillery — and a substantial navy. He was methodical, relentless, and understood that control of the coast and its harbours was inseparable from control of the land. Navarino Bay, sheltered and spacious, was the finest anchorage on the peninsula. In May, he moved to secure it completely. Paliokastro, the old fortress guarding the northern bay, and Sphacteria — the narrow island running along the bay's western edge, historically the key to controlling its entrance — were both in his sights simultaneously.

The Greek response was led by Captain Anastasios Tsamados, a veteran naval commander from Hydra, and Alexandros Mavrokordatos, one of the leading politicians of the Greek provisional government. Tsamados rushed to the defence with a small contingent of sailors and soldiers while Mavrokordatos coordinated from nearby. Against fifteen hundred Egyptian troops who landed on the island, Tsamados led a far smaller force. He was shot in the leg during the fighting. He continued to command. He was killed. Santarosa died in the same engagement, one of several European philhellenes who had come to the Peloponnese to fight for a cause they believed in. The island fell.

Mavrokordatos and the remaining Greek sailors made for their ship, the brig Aris, and attempted to sail out of the bay. Ibrahim's fleet — thirty-four ships — opened fire. For four hours the Aris was bombarded as she threaded through the gauntlet, suffering two dead and eight wounded before finally breaking free. The escape was desperate and costly, but the Aris survived. The loss of Sphacteria was not reversed: days later, the Greeks surrendered the nearby fortress of Neokastro (the New Navarino fortress at Pylos) to Ibrahim, giving him control of the bay and a mainland base he had been seeking for months.

The response came from Admiral Andreas Miaoulis, one of the war's most resourceful Greek commanders. Unable to challenge Ibrahim's superior fleet in open battle, Miaoulis turned to the fire ship — a weapon the Greeks had wielded with devastating effect since the earliest days of the revolution. In a desperate raid on the Egyptian fleet at Methoni, Miaoulis succeeded in destroying around ten ships, including a frigate and three corvettes. It was a bold stroke, and a painful one for Ibrahim. But it could not undo what had happened in the bay. The loss of Sphacteria and Neokastro meant Ibrahim now held the western Peloponnese's most important anchorage. The balance of the war had shifted — and would only shift back two years later, in the same bay, when a very different fleet arrived.

The Italian philhellenes who died in Greece — Santarosa among them — represent a particular current of European romanticism: the belief that liberty was not merely a national cause but a human one, worth crossing borders and risking everything to defend. Santarosa had been a minister, a revolutionary, an exile, and finally a soldier in someone else's war. His memorial stands on the shore of Sphacteria, placed there after the later Battle of Navarino made the island a site of commemorations. The memorial to the Russian dead of 1827 stands not far away, a small wooden Orthodox chapel. Between them, the island holds layers of sacrifice separated by two years and two different contests for the same water.