In the autumn of 1204, following their capture of Constantinople, the Crusaders under Boniface of Montferrat marched into Thessaly and headed south.
Sgouros withdrew before the superior Crusader army.
Initially he planned to make a stand in the pass of the Thermopylae, but he eventually retired to the Peloponnese, establishing a defence on the Isthmus of Corinth.
The army of Boniface took Boeotia and Attica without resistance, and relieved the blockade of Athens, where Choniates surrendered the city to him.
Boniface's first assault on Sgouros's defenses in the Isthmus was repulsed, but the second broke through, and by spring 1205 he controlled the countryside of the northeastern Peloponnese, while the fortified cities held out against him.

Sgouros himself withdrew and was blockaded in his stronghold, the well-fortified citadel of the Acrocorinth, in a siege that was to last five years.
Sgouros's resistance was energetic, with sorties that harassed the besiegers.
To tighten their siege, the Franks built two forts, one on the hill of Pendeskouphi and one on the eastern approaches.
According to legend, Sgouros eventually despaired, and in 1208 he jumped off the high cliffs on his horse.
Resistance was continued by a certain Theodore, but in the end, the citadel fell in 1210, removing one of the last major centers of resistance against the establishment of the Frankish Principality of Achaea.
In the autumn of 1204, following their capture of Constantinople, the Crusaders under Boniface of Montferrat marched into Thessaly and headed south. Sgouros withdrew before the superior Crusader army. Initially he planned to make a stand in the pass of the Thermopylae, but he eventually retired to the Peloponnese, establishing a defence on the Isthmus of Corinth. The army of Boniface took Boeotia and Attica without resistance, and relieved the blockade of Athens, where Choniates surrendered the city to him. Boniface's first assault on Sgouros's defenses in the Isthmus was repulsed, but the second broke through, and by spring 1205 he controlled the countryside of the northeastern Peloponnese, while the fortified cities held out against him.
Sgouros himself withdrew and was blockaded in his stronghold, the well-fortified citadel of the Acrocorinth, in a siege that was to last five years. Sgouros's resistance was energetic, with sorties that harassed the besiegers. To tighten their siege, the Franks built two forts, one on the hill of Pendeskouphi and one on the eastern approaches. According to legend, Sgouros eventually despaired, and in 1208 he jumped off the high cliffs on his horse. Resistance was continued by a certain Theodore, but in the end, the citadel fell in 1210, removing one of the last major centers of resistance against the establishment of the Frankish Principality of Achaea.
Leo Sgouros