During the regency of Empress Zoe in 913–919, Leo is recorded as being again Domestic of the Schools and holding the dignity of "magistros". In 917, he was placed in charge of a large-scale expedition against the Bulgarians. The plan involved a two-pronged assault, one from the south by the main Byzantine army under Leo Phokas, and one from the north by the Pechenegs, who were to be ferried across the Danube by the Byzantine navy under Romanos Lekapenos. In the event, however, the Pechenegs did not help the Byzantines, partly because Lekapenos quarrelled with their leader (or, as Runciman suggests, might have even been bribed by the Bulgarians) and partly because they had already begun plundering on their own, disregarding the Byzantine plan. Left unsupported by both the Pechenegs and the fleet, Phokas suffered a crushing defeat at the hands of Tsar Symeon at the Battle of Acheloos. The imperial army was almost annihilated, and Phokas himself barely escaped. As Symeon marched south towards the imperial capital, Constantinople, Phokas gathered a motley force and attempted to halt his advance, but was again defeated by Symeon in a surprise night attack at Katasyrtai.