Saxon colonization into the region from the 5th to the 8th centuries likely extended the linguistic border somewhat south and west so that by the 9th 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 place names (toponyms) and family names (patronyms) of the region. Beginning in the 9th century, the linguistic border began a steady move to north and the east, and by the end of the 15th century Romance dialects had totally displaced the Dutch.
Pas-de-Calais is one of the original 83 departments created during the French Revolution on March 4, 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 empire.
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.
The principal rivers are the following:
Pas-de-Calais is one of the most heavily populated departments of France, and yet it has no large cities. Calais has only about 80,000 inhabitants, followed closely by Boulogne-sur-Mer and Arras. The remaining population is primarily concentrated along the border with the department of Nord in the mining district, where a string of small towns constitutes an urban area with a population of about 1.2 million. The center and south of the department are more rural, but still quite heavily populated, with many villages and small towns.
Although the department saw some of the heaviest fighting of World War I, its population rebounded quickly after both world wars. However, many of the mining towns have seen dramatic decreases in population, some up to half of their population.