Original: But this gain was not without its loss, as Sempronius avoided Hannibal's watchfulness, slipped around his flank, and joined his colleague in his camp near the Trebia River near Placentia.
Simplified: Sempronius avoided Hannibal and joined Scipio near the Trebbia River near Placentia. At Trebia, Hannibal deafeated the Roman infantry by a surprise attack from an ambush in the flank.