From its source at Sommaisne en Argonne between the Meuse and the Marne, the Aisne, Caesar's Axona, runs northwest until it reaches Vouziers where it takes a wide turn and runs due west to its confluence with the Oise at Compiègne (Oise), almost 300 km from its source. Its passage through the Ardennes is a tortuous one and the oxbow lakes it has left behind tell the story of its meanderings across the flatlands around Rethel. Although it was partially canalised in the 1830s, it can still be the cause of impressive floods, its waters suddenly overwhelming the plain and flooding the valley villages. These convulsions give the river a new course once again, washing away earlier meanders and creating temporary islands, in stark contrast with its summer tranquillity. Lush meadows run along the banks of the river, their moist soils providing excellent grazing for livestock.

Only a few traces of Palaeolithic occupation have been found. These take the form of double-sided stone tools, generally found in gravel pits dug alongside the river in the Porcien area. While the Neolithic era has been comprehensively studied in the Soissons region by the government research body URA 12, the region around Rethel has been left largely untouched. The few discoveries made there, however, have provided evidence of sedentary settlements from 5,000 BCE on the lowest alluvial terraces.