Quick Explanation of Moorish Castle built in 725AD at Gibraltar

The Moorish Castle at Gibraltar is supposed to have been built around 725 AD, that is what the inscription above the previous gate had said, according to the book The History of the Late Siege of Gibraltar by Sir John Drinkwater published in 1785.
I’ve just noticed today how the walls from Casemates Square connect to other walls that lead up to The Moorish Castle.