Their culture was a spartan one; they purportedly would not partake of alcoholic beverages or any other such luxury, feeling that the mind must remain clear to be brave. Records indicate that they had no trade or merchant class of any kind, which would lead to the assumption that they had no currency, and were probably not very rich or advanced people.
Aided by the Atrebates and Viromandui and numerous other German tribes, they came very close to defeating Caesar in 57 BC. The Atuatuci, another tribe, were marching to join them but did not reach the battle in time, leading to defeat. After this battle most of the tribes of Belgea surrendered, but the Nervii did not, supposedly decrying the states that had given up as traitors and vowed not to accept peace or ambassador from Rome. Indeed, they continued harassing Roman baggage trains. Caesar devised a plan to exploit the Nervians lack of cavalry, which apparently succeeded. After further decimation by the Romans, they were brought to their knees, and begged for an armistice. Records claim there situation was such that their army of 60,000 had been cut down to 500, and their 600 senators reduced to 3. Supposedly, Caesar granted them the peace they wanted, and bade their neighbors to show no anger towards them.
The Nervii’s capital city seems to have been at Bagacum, also known as Bavay.
All figures taken from "Gallic_Wars" By Julius Caesar, of all people. Because of this rather ubiquitous author, some aspects of this may be tilted to make Caesar look better, but the basic elements can be taken as fact.