Although the early history of habitation in the area is obscure, the Romans called the settlement Caletum. Julius Caesar mustered 800 to 1000 sailing boats and 5 legions and some 2000 horses at Calais due to its strategic position to attack Britannia] Later, in medieval times, the settlement was inhabited by people who spoke Dutch, and who called it Kales. It is mentioned in Welsh documents as Caled, in Irish documents as Calad, and in Breton documents as Kaled. It is at the western edge of the early medieval estuary of the River Aa. As the pebble and sand ridge extended eastwards from Calais, the haven behind it developed into fen, as the estuary progressively filled with silt and peat. Subsequently, canals were cut between Saint-Omer, the trading centre formerly at the head of the estuary and three places to the west, centre and east on the newly formed coast, respectively Calais, Grave lines and Dunkirk. At some time prior to the 10th century it would have been a fishing village on a sandy beach backed by pebbles and a creek, It was improved by the Count of Flanders in 997 and fortified by the Count of Boulogne in 1224.
The first document mentioning the existence of this community is the town charter granted by Mathieu d'Alsace in 1181 to Gerard de Guelders, Count of Boulogne; Calais became part of the county of Boulogne. In 1189, Richard the Lion heart is documented to have landed at Calais on his journey to the Third Crusade.
The English needed a foothold on the continent to serve as a trading centre, mainly for exports of English wool to farther European destinations and to compete with the marts of the low-countries, through which much of this trade had formerly been conducted. It was largely due to French interference in this vital trade, that the campaign was fought, which culminated in the Battle of Crécy which commenced on 4 September 1346. The town was most conveniently situated