I have not seen many pictures of castles with moats. I wonder how they kept the moat full, unless a nearby brook could be diverted. Castles were sometimes located on small islands to make them hard to attack. But more often they were on high places which are easiert to defend. Of course an abundant xource of stone was essential. And building them on a big rock meant they could not be undermined.But a well had to be available where enemy could not get control of it in a siege.