Martigny enters History In winter 57-56 BC Cesar, in Gallic Wars, describes the battle which took place in a small market town that he called Octodurus and which opposed a legion under Servius Galbaand and inhabitants from the region, the Veragri, assisted by the Seduni from Central Valais. According to the Great General, Romans remained in control of the land; after having set alight the indigenous town, divided up by the Dranse river, they however had to withdraw to winter in the Allobroges country, already under their authority. Cesar justifies his intervention by the fact that the tradesmen who were taking the Gd St-Bernard pass were subject to serious dangers and had to pay heavy tolls. But certainly strategic purposes were the actual reasons: Cesar wanted to control the most direct way between Italy and Great Britain, north Gaul and the Rhine countries. When the Romans left, the fortified gallic village was rebuilt. Integration of Valais to the Empire happened some years later, by 15 BC.

In relation to the Great Britain conquest which he undertook at the beginning of his reign, Emperor Claude I (41-54 AD) created at the foot of the Gd St-Bernard pass, away from Octodurus (which exact location is still unknown to us), a new town called Forum Claudii Vallensium (Valais Claude's market).
This town became the capital of the Vallis Poenina (the Valais), province often joined to the Tarantaise, on the western side of the Pt St-Bernard pass, under the authority of the same imperial governor residing equally at Aime ((Forum Claudii Ceutronum) and at Martigny. Road stop and important market along the pass road, headquarters of Valais authorities and of the imperial administration, the small size city was flourishing until the 4th century. No outstanding event punctuates it's history except troops and soldiers passing through ( though not stationing), in particular in 69 AD.

Several causes resulted in its abandon, at the end of the 4th century: economic decay, road insecurity, "barbarian" incursion threats, lack of ramparts… Initially the centre of the religious but also political and economic activities, apparently moved around the actual parish church where a first Christian sanctuary had developed; the latter was quickly transformed into a cathedral, probably that of the Valais first known bishop, Saint-Theodore who, in 381 signed the Aquilee Council Acts in quality of "episcopus octodorensis".
Before 585, this Episcopal seat was transferred to Sion, central location to the valley scale and easily defensible, whereas Forum Claudii Vallensium, capital of the roman Valais to the scale of the international way to the Gd St- Bernard pass, always remained an open town.