Calais history may have been dating to ancient times, but evidence of human settlements is from the Roman era when it was known as Caletum. It was a part of a Dutch-speaking area of France in medieval times. It is the last exit point of France and the first northern entry point from England; it bloomed into an important port when it was a fishing village in the 10th century. By the 13th century in 1224, it was fortified by the Count of Boulogne.
Due to its strategic location and importance in ferry transport with Dover, the port of Calais was constantly hounded to grab for trade business. Edward assumed himself to be the heir to the Kingdom of France after his uncle Charles IV's death in 1328. Calais was invaded by King Edward III of England in 1347 and seized after an eleven month-long Battle of Crecy where the locals lost their town.
As an act of revenge, King Edward demanded payback from the local people for not surrendering to him immediately during the battle. He ordered for mass eradication of the population, and they would be spared if six principal citizens of the town surrendered themselves to die. But upon Queen Philippa of Hainault request, the six of them were spared. This historical episode is reconstructed in the form of statues of The Burghers of Calais (Les Bourgeois de Calais) erected in 1888 and created by famous sculptor Auguste Rodin.
Later on, King Edward expelled most of the French citizens and settled the town with English people.
With the Treaty of Brétigny in 1360, Guînes, Marck and Calais, jointly known as "Pale of Calais", was unofficially allotted to the English rule. In 1363 it became an important port and in 1372 became a constituency of the Parliament of England. But it did keep its bonding with France as it still was a part of the diocese of Therouanne.
Calais became the "brightest jewel" in the English crown as the port revenues amounted to 1/3rd of England's revenue. Primarily, tin, lead, cloth and wool were the main trade items. Nearly half of the population of Calais was connected to the wool trade.
For many years Calais remained a vital part of the English Parliament, with its representative being a part of the government. But it was turning out to be an expensive proposition to maintain Calais as it didn't have any natural defences and so had to depend on man-made fortifications.
The border of Calais and Franco-Burgundy were the same, so there was a constant threat of attack from French and Duchy of Burgundy forces. Both the French and Duchy of Burgundy hated each other so much that they preferred Calais with England rather than part of each other's constituency. But finally, the French overtook the Burgundy and incorporated it into France.
When Francis, Duke of Guise, took over the throne of France, he took benefit of the disadvantage that Calais had regarding natural defences. On January 1, 1958, the English lost their rule over Calais. The French attacked Calais at the city's weak point of Fort Nieulay and its gates that could have sent the French back when opened. But the gates remain closed, thus surprising the English. Calais (then known as Calaisis) was renamed the Pays Reconquis, and the Dutch citizens were forced to speak French. The city came under Spanish rule for a short period from 1596-1598. It was later returned to the French under the Treaty of Vervins.
During World War II, Calais was devastated by the German and French troops. In the War of Siege of Calais in 1940, which preceded Operation Dynamo, the 10th Panzer Division German forces held out for many days at the city against French and English allied forces. This led to the bombing and precise attacks by both sides of the forces, leading to the destruction of the city.
During the German occupation, it was heavily fortified and used as a base for launching flying bombs and placement for railway guns. But despite all the preparations, the Allied forces planned their attack well and bombed Calais heavily, and with the help of Canadian forces, Calais was liberated in 1944.
Around 1999, illegal immigrants from Africa, Syria, Iraq started to arrive in Calais. They were trying to enter the UK. The UK blamed France for the migrants and they supplied fencing to prevent migrants from entering the UK. As a result, migrants started living in Calais.