Actually, mine was the Pontcysyllte aqueduct near Llangollen, and it does have a river underneath it too, but i'll admit, neither the canel or the river are as wide as the one in Germany.
My point was, canals over rivers are not that new (even Wales has a few!).
If your mind boggled at the German one, you should try going over one in a canal boat. Suddenly having a sheer 100ft drop appear by the side of your boat is pantscrappingly terrifying.