Short answers, pulled from the story.
Emperor Caligula ordered the construction of a tall lighthouse at Gesoriacum in 39 AD. This structure stood for over sixteen hundred years before coastal erosion caused it to topple into the sea in 1644.
A Celtic tribe known as the Boii founded the original settlement called Gesoriacum. The name changed from Gesoriacum to Bononia sometime between the sack in 293 and 310.
France bought back Boulogne for 400,000 crowns under the terms of the Peace of Boulogne in 1550. English forces had occupied the town again from 1544 to 1550 prior to this transaction.
Napoleon amassed La Grande Armée here for several months during 1805 to prepare for an invasion of the United Kingdom. A column commemorates the gathering of 200,000 soldiers near the harbor for that proposed attack.
On the 22nd of May 1940, two British Guards battalions attempted to defend the city against the German 2nd Panzer Division during the Battle of France. Survivors were evacuated by Royal Navy destroyers under direct German gunfire.
The city functions as France's largest fishing port specializing primarily in herring catches. Seven thousand inhabitants derive part or all of their livelihoods directly from fishing activities today.