Most major ports have been defended since their inception and Calais is no exception with a series of small forts built around the strategic location.
At this location at the heart of the port entrance it was Fort Risban which proved the defences. What makes this fort unusual though is that it was originally built by the English in 1346 and initially constructed to prevent supplies reaching the besieged, French-controlled town by sea. Through several upgrades it remained in English hands for over 200 years before the town was recaptured by the French in 1558.
When German forces occupied northern France in 1940, the fort area was used as shelter for troop and several additional concrete constructions were added, although only one survives today due to the expansion of the port area with housing, hotels, and public attractions.
The bunker here is a large R643 type which boated a three embrasure armoured cupola to enable it to have a wide arc of fire over the area.
The steel turret was removed for scrap at the end of the war and the defensive Tobruk was destroyed, but you can still see the rest of the building including the once armoured embrasure which could focus fire into the mouth of the port.