Such vestiges prove that Neomagus must have been a place of importance; and, like the other Gallo-Roman cities, it would probably have maintained its honors under the Franks; but about the middle of the fourth century, the Saxons, swarming from the mouths of the Elbe and Weser, laid waste the coasts of Belgium and of Neustria, and finally established themselves in that portion of northern Gaul called the Secunda Lugdunensis, which thence obtained, in the Notitia Imperii, the title of the Littus Saxonicum.—In the course of these incursions, it is supposed that Neomagus was utterly destroyed by the invaders. None of the medals dug up within the precincts of the town, or in its neighborhood, bear a later date than the reign of Constantine; and, though the city is recorded in the Itinerary of Antoninus, no mention of it is to be found in the curious chart, known by the name of the Tabula Peutingeriana, formed under the reign of Theodosius the Great; so that it then appears to have been completely swept away and forgotten.
The new town of Lisieux and the bishopric most probably arose together, towards the close of the sixth century; and the city, like other provincial capitals in Gaul, took the name of the tribe by whom the district had been peopled. It first appears in history under the appellation of Lexovium or Lexobium: in the eleventh century, when Ordericus Vitalis composed his history, it was called Luxovium; and soon after it became Lixovium, and Lizovium, which, gallicised, naturally passed into Lyzieulx, or, as it is now written, Lisieux. The city was ravaged by the Normans about the year 877, in the course of one of their predatory excursions from Bayeux: it again felt their vengeance early in the following century, when Rollo, after taking Bayeux by storm, sacked Lisieux at the head of his army on his way to Rouen. The conqueror was not put in possession of the Lexovian territory by Charles the Simple till 923, eleven years after the rest of Neustria had been ceded to him.