The Greek War of Independence had been under way since March 1821. By August, Greek revolutionary forces had encircled Tripolitsa — the Ottoman administrative center of the Morea, seat of the governor and a heavily garrisoned city — but taking it by direct assault was beyond their means. Siege warfare required patience and blockade. The Ottomans inside needed supplies and knew it. Their response was night sorties: armed columns breaking out of the city to raid villages, seize provisions, and probe for weaknesses in the Greek encirclement.

When Kolokotronis took command of the siege, he recognized the pattern. The Ottomans were predictable in their routes and their objectives. A sufficiently positioned obstruction, with Greek fighters behind it, could turn an Ottoman sortie into a trap. He ordered the trench dug, and the villagers dug it.

During the night of 9–10 August, an Ottoman force of 3,000 infantry and cavalry broke out from Tripolitsa and moved toward Loukas hill, where the Greek chieftain Ioannis Dagres held his position. They raided villages in the surrounding area — seizing what they could — then struck Dagres's force at dawn, pushing the Greeks into difficulty.

Kolokotronis, reading the situation quickly, dispatched orders across the field: Plapoutas, Dimitrios Deligiannis, Papazafiropoulos, Christopoulos, George Aulakos, and the armed Greeks of Tripolitsa were to occupy positions within the trench. Other fighters went in behind the vineyard fences. Kolokotronis also ordered a diversionary thrust — forces under Demetrios Ypsilantis, Anagnostaras, and Panagiotis Giatrakos were to press the Ottomans from another direction, relieving pressure on Dagres.

The Ottoman forces under Ali Bey, having pushed Dagres back, realized they were at risk of being cut off. They began to withdraw — and withdrew directly into the trench line, where Greek fighters were waiting.

The Ottoman garrison cavalry came to the support of the retreating foot soldiers. Neither the infantry nor the cavalry could cross the trench cleanly under fire. Both suffered heavily in the attempt. The garrison then sent additional forces out from Tripolitsa to rescue the men in trouble, widening the engagement into a two-front fight. Kolokotronis moved between positions with his bodyguard, steadying his fighters and managing the flow of the battle. In the end, the Ottoman forces broke and fell back in disorder toward the city walls.

The losses were not equal. The Ottomans lost approximately 400 men — most of them killed at or near the trench line during the crossing attempts. Among the dead were Abdul Bölükbaşı, son of the local lord Sheikh Tahir Efendi, and Kabır Kehaya. Ali Bey himself survived the battle but died of his wounds three days later. The Ottomans also abandoned their animal carts and provisions on the field.

On the Greek side, thirty men were killed, including Thanasis, the brother of Ioannis Dagres. Several others were wounded, among them the minor leaders Apostolis Kolokotronis and Georgios Dritsas; Dritsas died of his wounds in the days that followed.

The Battle of the Trench did not end the siege of Tripolitsa. That would come on September 23, 1821, when the city finally fell — an event with consequences that extended far beyond the military. But the August engagement mattered. The Ottoman garrison had tried and failed to break the Greek grip on the city's supply lines. The losses were significant; the ability to forage outside the walls was now severely constrained. Morale inside the city declined sharply.

Kolokotronis understood what a prepared position could do against cavalry and formed infantry in the landscape around Tripolitsa — rocky, vineyard-divided terrain that undermined Ottoman tactical advantages. The trench was a tool suited to the land. It worked because the peasants who dug it knew that land, and because Kolokotronis had the strategic patience to prepare a trap rather than simply respond to each sortie in kind.