In the year 700 AD, two Irish princes, Lugli and Luglien, were on a pilgrimage to Rome. On the road between Boulogne and Thérouanne, near Ferfay, they were attacked and killed by robbers. Their servants buried the bodies, but they were moved by a storm to the castle of the Bishop of Thérouanne. This was seen to be a miracle. When the Normans invaded, the bodies, now holy relics, were moved to a safer place on an island with a marsh all around it. Years later, the sister of the princes, Lilia, came to pray at the chapel built to hold the relics. The town was named Lillers, after her.