Armorica, (from Celtic ar, “on,” and mor, “sea”), Latin name for the northwestern extremity of Gaul, now Brittany. In Celtic, Roman, and Frankish times Armorica also included the western part of what later became Normandy. In Julius Caesar’s time it was the home of five principal tribes, the most important being the Veneti. Under the Roman Empire it formed part of the province of Gallia Lugdunensis. It received many immigrants from the British Isles in the 5th and 6th centuries, during the time of the Saxon invasion.