 The largest island in the river, the "Île de la Cité" ("Island of the City"), was the easiest place to build bridges across the Seine; it became the crossing point on the important north-south trade route between Orléans and Flanders.The island was also the easiest place to defend; it gave the Parisians a sanctuary when the city was attacked by the Huns in the 5th century and Vikings in the 9th century.The Roman prefects had built their residences on the west end of the island; the first royal palace was built on the same site in the early Middle Ages.