He noted that the Belgae, were "the bravest, because they are furthest from the civilization and refinement of [our] Province, and merchants least frequently resort to them, and import those things which tend to effeminate the mind; and they are the nearest to the Germans, who dwell beyond the Rhine, with whom they are continually waging war".

The cultural cohesion of Belgium as Caesar sketched it is suggested by the maintaining of these borders, more or less, in administrative divisions (pagi) mapped out later by the Romans and still evident in the parishes of the Carolingian era.

[16] Archaeology suggests cultural continuities from the third through the first centuries BC within this subregion, inhabited in the time of Caesar by Bellovaci, Ambiani, Atrebates, and Veromandui.

[19] Around this same time, a characteristic form of enclosed sanctuary began to be built, and from the late 2nd through the mid 1st centuries BC, fortifications with a high earthen rampart and a wide, flat-bottomed ditch are concentrated there.

[29][30] For example, Maurits Gysseling suggested that prior to Celtic and Germanic influences the Belgae may have comprised a distinct Indo-European branch, termed Belgian.

[30] However, most of the Belgic tribal and personal names recorded are identifiably Gaulish, including those of the Germani cisrhenani, and this is indeed also true of the tribes immediately over the Rhine at this time, such as the Tencteri and Usipetes.

[31] The Romans were not precise in their ethnography of northern barbarians: by "Germanic", Caesar may simply have meant "originating east of the Rhine" (the homeland of the Germani cisrhenani) with no distinction of language intended.

[32] However, studies of place names, such as those of Maurits Gysseling, have been argued to show evidence of the pre-Roman presence of early Germanic languages throughout the Belgic area north of the Ardennes, where the Germani cisrhenani lived.

[33] Strabo also says that "Augustus Caesar, when dividing the country into four parts, united the Keltae to the Narbonnaise; the Aquitani he preserved the same as Julius Caesar, but added thereto fourteen other nations of those who dwelt between the Garonne and the river Loire, and dividing the rest into two parts, the one extending to the upper districts of the Rhine (Gallia Lugdunensis) he made dependent upon Lugdunum, the other [he assigned] to the Belgae (Gallia Belgica).

Edith Wightman proposed that Caesar can be read as treating only the southwestern Belgic tribes, the Suessiones, Viromandui and Ambiani and perhaps some of their neighbours, as the true ethnic Belgae, as opposed to those in a political and military alliance with them.

She reads Caesar as implying a "transition zone" of mixed ethnicity and ancestry for the Menapii, Nervii and Morini, all living in the northwest of the Belgic region, neighbours to the Germani cisrhenani in the northeast.

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.

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).

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.

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).

The arrival and spread of Aylesford-Swarling pottery across the southeastern corner of Britain has been related to the Belgic invasion since Arthur Evans published his excavation of Aylesford in 1890,[41] which was then thought to show "the demonstrable reality of a Belgic invasion", according to Sir Barry Cunliffe, although more recent studies tend to downplay the role of migration in favour of increasing trade links; the question remains unclear.

[42] A large number of coins of the Ambiani dating to the mid-second century BC have been found in southern Britain and the remains of a possible Belgic fort have been unearthed in Kent.

Commius of the Atrebates, Caesar's former ally, fled to Britain after participating in Vercingetorix's rebellion and either joined or established a British branch of his tribe.

Based on the development of imagery on coins, by the time of the Roman conquest, some of the tribes of south-eastern Britain likely were ruled by a Belgic nobility and were culturally influenced by them.

[47][48] Fintan O'Toole suggested the Keshcarrigan Bowl is evidence for the movement of people into Ireland following upheaval and displacement, triggered by the Belgae arriving into Britain as refugees.