This is the moat around the alcazar. He told us the name in spanish but I don't actually remember. Since the alcazar is the fortress on a hill you would have needed to either climb the wall around the city or go across the bridge over the moat to get in. This means that the city was completely protected at night! Much like the movies we see from the middle ages. Our guide also said that if the king didn't like you you got thrown in the moat... he was joking... i think.