Chronology of the Late Roman Antiquity walls of Le Mans (France) by OSL, archaeomagnetism and radiocarbon

•The best-preserved example of Late Roman Antiquity urban fortification in Gaul.•40 dates by 14C, OSL, single grain OSL and archaeomagnetism on bricks and mortars.•The comparison of bricks and mortars dates provides no evidence of brick reuse.•Bayesian modelling dates the construction of the walls in [301; 423] CE (95%).•The construction occurred in a stable political context.