The Pas-de-Calais (, "strait of Calais"; ; also ) is a department in northern France named after the French designation of the Strait of Dover, which it borders. It has the most communes of all the departments of France, 890, and is the 8th most populous. It had a population of 1,465,278 in 2019. The Calais Passage connects to the Port of Calais on the English Channel. The Pas-de-Calais borders the departments of Nord and Somme and is connected to the English county of Kent via the Channel Tunnel. History Inhabited since prehistoric times, the Pas-de-Calais region was populated in turn by the Celtic Belgae, the Romans, the Germanic Franks and the Alemanni. During the fourth and fifth centuries, the Roman practice of co-opting Germanic tribes to provide military and defence services along the route from Boulogne-sur-Mer to Cologne created a Germanic-Romance linguistic border in the region that persisted until the eighth century. Saxon colonization into the region from the fifth to the eighth centuries likely extended the linguistic border somewhat south and west so that by the ninth century most inhabitants north of the line between Béthune and Berck spoke a dialect of Middle Dutch, while the inhabitants to the south spoke Picard, a variety of Romance dialects. This linguistic border is still evident today in the toponyms and patronyms of the region. Beginning in the ninth century, the linguistic border began a steady move to north and the east, and by the end of the 15th century Romance dialects had completely displaced those of Dutch. Pas-de-Calais is one of the original 83 departments created during the French Revolution on 4 March 1790. It was created from parts of the former provinces of Calaisis, formerly English, Boulonnais, Ponthieu and Artois, this last formerly part of the Spanish Netherlands. Some of the costliest battles of World War I were fought in the region. The Canadian National Vimy Memorial, eight kilometres from Arras, commemorates the Battle of Vimy Ridge assault during the Battle of Arras (1917) and is Canada's most important memorial in Europe to its fallen soldiers. Pas-de-Calais was also the target of Operation Fortitude during World War II, which was an Allied plan to deceive the Germans that the invasion of Europe at D-Day was to occur here, rather than in Normandy. Geography Pas-de-Calais is in the current region of Hauts-de-France and is surrounded by the departments of Nord