Caesar realized an opportunity was presenting itself: if he could beat the men from the army home, he could take their lands with ease. His armies' travel speed proved to be a crucial aspect of his ensuing victories. He rushed to the Suessiones' "oppidum" at what is now Villeneuve-Saint-Germain and laid siege to it. The Belgic army nullified Caesar's advantage by sneaking back into the city under cover of darkness. The Roman siege preparations proved to be the decisive factor: grand Roman-style siege warfare was unknown to the Gauls, and the might of the Roman's preparations drove the Gauls to surrender promptly. This had a ripple effect: the nearby Bellovaci and Ambiones surrendered immediately afterward, realizing the Romans had defeated a powerful army without any combat. Not all the tribes were so cowed, however. The Nervii allied with the Atrebates and Viromandui, and planned to ambush the Romans. The ensuing battle of the Sabis was nearly a humiliating defeat for Caesar, and the Roman victory was very hard won.