In the southern part of the Biturige territory, about 100 kms south-west of their capital, Avaricum, the oppidum of Argentomagus was established. The site occupied a roughly square plateau with rounded corners spreading out over an area of 27 hectares.

Second in size of all the oppida in the Berry, this site, defended to the south by the high cliffs overlooking the Creuse, to the east by the steep slopes plunging down to the La Mage brook and to the west by a dried-up valley, was additionally protected by formidable double ramparts and an external ditch.

On the north-west side, the remains of the only entrance are still perfectly discernible. This gate, known as "à ailes rentrantes", was protected by a long, wide, diagonal trench which forced any potential attacker a further eighty metres forward onto the exposed right flank.

Inside the oppidum, signs of the Gaulish period are hardly in evidence. A few structures date back to the second half of the 1st century BC though some indubitably Gaulish artifacts have been recovered: bronze sieves, Nauheim fibulae, threadlike iron fibulae, bracelets made from schist, glass and amber beads and a bronze belt buckle typical of the late Tène period.