The Greek Army under Demetrios Ypsilantis which for the first time trained to fight as a regular European army rather than as guerilla bands, awaited Aslan Bey's forces at Petra, a town at a narrow passage in Boeotia between Livadeia and Thebes in order to dispute their passage. On September 12, 1829 the two armies engaged in battle. The Greeks, after a hail of gunfire, charged with swords and drove the Ottoman army into a disorderly retreat.