Fortifications of Zwolle
Enclosed City of Zwolle, the Netherlands, from a facsimile publication of the Blaeu's Toonneel der Steden, 1652.
Note the river was made the source of the water filling the moat system, but that the defenses were built on both sides of the river, not using the river itself as an outside barrier. Note also for anyone to get into Zwolle, there were only three bridges, all drawbridges.