Haguenau is a commune in the Bas-Rhin department of France, of which it is a sub-prefecture. It is second in size in the Bas-Rhin only to Strasbourg, some 30 km to the south. To the north of the town, the Forest of Haguenau is the largest undivided forest in France. Haguenau was founded by German dukes and has swapped back and forth several times between Germany and France over the centuries, with its spelling altering between "Hagenau" and "Haguenau" by the turn.