Caesar conquered the Belgae, beginning in 57 BC. He writes that the Belgae were conspiring and arming themselves in response to his earlier conquests; to counter this threat, he raised two new
legions and ordered his Gallic allies, the
Aedui, to invade the territory of the
Bellovaci, the largest and fiercest of the Belgae tribes. Wary of the numbers and bravery of the Belgae, Caesar initially avoided a pitched battle, resorting mainly to
cavalry skirmishes to probe their strengths and weaknesses. Once he was satisfied his troops were a match for them, he made camp on a low hill protected by a marsh at the front and the river
Aisne behind, near Bibrax (between modern
Laon and
Reims) in the territory of the Remi. The Belgae attacked over the river, but were repulsed after a fierce battle. Realising they could not dislodge the Romans and aware of the approach of the Aedui into the lands of the Bellovaci, the Belgae decided to disband their combined force and return to their own lands. Caesar's informants advised him that whichever tribe Caesar attacked first, the others would come to their defence. They broke camp shortly before midnight. At daybreak, satisfied the retreat was not a trap, Caesar sent cavalry to harass the rear guard, followed by three legions. Many of the Belgae were killed in battle. Caesar next marched into the territory of the Suessiones and besieged the town of Noviodunum (
Soissons). Seeing the Romans'
siege engines, the Suessiones surrendered, whereupon Caesar turned his attention to the Bellovaci, who had retreated into the fortress of Bratuspantium (between modern
Amiens and
Beauvais). They quickly surrendered, as did the Ambiani. The
Nervii, along with the Atrebates and Viromandui, decided to fight (the Atuatuci had also agreed to join them, but had not yet arrived). They concealed themselves in the forests and attacked the approaching Roman column at the river Sabis (previously thought to be the
Sambre, but recently the
Selle is thought to be more probable). Their attack was quick and unexpected. The element of surprise briefly left the Romans exposed. Some of the Romans did not have time to take the covers off their shields or to even put on their helmets. However, Caesar grabbed a shield, made his way to the front line, and quickly organised his forces. The two Roman legions guarding the baggage train at the rear finally arrived and helped to turn the tide of the battle. Caesar says the Nervii were almost annihilated in the battle, and is effusive in his tribute to their bravery, calling them "heroes" (for more details see
Battle of the Sabis). The Atuatuci, who were marching to their aid, turned back on hearing of the defeat and retreated to one stronghold, were put under siege, and soon surrendered and handed over their arms. However, the surrender was a ploy, and the Atuatuci, armed with weapons they had hidden, tried to break out during the night. The Romans had the advantage of position and killed 4,000. The rest, about 53,000, were sold into slavery. In 53 BC, the Eburones, led by
Ambiorix, along with the Nervii, Menapii and Morini, revolted again and wiped out fifteen cohorts, only to be put down by Caesar. The Belgae fought in the uprising of
Vercingetorix in 52 BC. After their final subjugation, Caesar combined the three parts of Gaul, the territory of the Belgae, Celtae and Aquitani, into a single unwieldy province (
Gallia Comata, "long-haired Gaul") that was reorganized by the emperor
Augustus into its traditional cultural divisions. The
province of
Gallia Belgica was bounded on its east by the Rhine and extended all the way from the North Sea to
Lake Constance (
Lacus Brigantinus), including parts of what is now western Switzerland, with its capital at the city of the Remi (Reims). Under
Diocletian,
Belgica Prima (capital Augusta Trevirorum,
Trier) and
Belgica Secunda (capital
Reims) formed part of the
diocese of Gaul. ==Belgae outside Gaul==