OK... the towers part, I have no idea ). The map in the original Serbian article should help you out though. But I think I know what is confusing you. There are 3 parts of the fort. The foward, back, and the upper city. The forward city is comprised of TWO parts, the upper and the lower. This "upper" part of the forward city is NOT the upper city. Here:

Forward city (the lowest, X axis)
Upper part (higher, Z axis)
Lower part (lower, Z axis)
Back city (higher than forward, X axis)
Upper city (higher, completely at the back, X axis)

That's how I'm reading it, and I'm pretty sure I'm right. And if you look at the map, tower 1 is in the upper city, and it's what the word 'citadel' is referring to. Now the moat... in the Serbian article, the present tense is used ("jer je povezan sa Dunavom"), so the moat is still connected, BUT the Danube is not filling it with water now ("koji ga je verovatno punio", trns. "which probably filled it with water").