Short answers, pulled from the story.
Calais is 34 km from the English coast at the Strait of Dover, the narrowest point in the English Channel. The White Cliffs of Dover are visible from Calais on a clear day. The Channel Tunnel has connected Calais to Folkestone since 1994.
Calais was under English control from 1347, when Edward III captured it after a siege, until 1558, when French forces led by Francis, Duke of Guise, retook the city. That is roughly 211 years of English rule.
Les Bourgeois de Calais is a bronze sculpture by Auguste Rodin depicting six leading citizens who offered their lives to Edward III in 1347 to save the rest of the town's population from execution. Rodin based his design on a fourteenth-century account by Jean Froissart and intended to evoke sympathy by emphasizing the men's pained expressions. The cast was erected in Calais in 1895, funded by a public grant of 10,000 francs.
During the siege of Calais from the 22nd to the 27th of May 1940, a force of 3,000 British and 800 French troops held out against the German 10th Panzer Division. This kept the 10th Panzer occupied and away from the Dunkirk perimeter, potentially enabling the evacuation of some 330,000 Allied troops between the 26th of May and the 4th of June 1940.
Calais earned this description because of its enormous economic importance as a gateway port for the tin, lead, cloth, and wool trades. Its customs revenues at times amounted to a third of the English government's total income, with wool the dominant commodity by far.
The Calais jungle is the nickname for a series of makeshift camps that formed near Calais from 1999 onward, housing migrants and asylum seekers from Darfur, Afghanistan, Syria, Iraq, Eritrea, and other regions who were attempting to enter the United Kingdom. French authorities cleared the main camp on the 26th of October 2016, but a migrant presence has remained in Calais ever since.