When the Castillo was at the peak of its spiny Spanish defensive mode, the moat, though kept dry, was a deep, perplexing obstacle for any who might wish the fort ill. During times of British siege, cattle were kept in the moat, which could be fetched through sallyports for the purpose of feeding the fort's inhabitants. Though one is rather tersely instructed to KEEP OFF MOAT STAIRS today, this is how the moat would have been accessed in dayes of olde. Hopefully the cattle weren't expected to descend these stairs?!