This quarter's altitude varies from about . In Orléans, the Loire is separated by a submerged dike known as the "dhuis" into the "Grande Loire" to the north, no longer navigable, and the "Petite Loire" to the south. This dike is just one part of a vast system of construction that previously allowed the Loire to remain navigable to this point. The Loire was formerly an important navigation and trading route. With the increase in size of ocean-going ships, large ships can now navigate the estuary only up to about Nantes. Boats on the river were traditionally flat-bottomed boats, with large but foldable masts so the sails could gather wind from above the river banks, but the masts could be lowered in order to allow the boats to pass under bridges. these vessels are known as "gabarre," "futreau," and so on, and may be viewed by tourists near pont Royal. The river's irregular flow strongly limits traffic on it, in particular at its ascent, though this can be overcome by boats being given a tow. An "Inexplosible"-type paddle steamer owned by the mairie was put in place in August 2007, facing Place de la Loire and containing a bar. Every two years, the Festival de Loire recalls the role played by the river in the commune's history. On the river's north bank, near the town centre, is the Canal d'Orléans, which connects to the Canal du Loing and the Canal de Briare at Buges near Montargis. The canal is no longer used along its whole length. Its route within Orléans runs parallel to the river, separated from it by a wall or "muret", with a promenade along the top. Its last pound was transformed into an outdoor swimming pool in the 1960s, then filled in. It was reopened in 2007 for the "fêtes de Loire." There are plans to revive use of the canal for recreation and install a pleasure-boat port there. Orléans experiences an oceanic climate (Köppen climate classification "Cfb"), similar to much of central France. Cenabum was a Gallic stronghold, one of the principal towns of the tribe of the Carnutes where the Druids held their annual assembly. The Carnutes were massacred and the city was destroyed by Julius Caesar in 52 BC, then a new city was built on its ruins by settlers from the gens Aurelia who named the city, civitas Aurelianorum ("city of the Aurelii"), after themselves.