Deserted Oasis of Ayn Umm al-Dabaqi in Egypt

A remarkably complete, mud-brick fortress which probably dates from between he 10th and 12th centuries. It certainly includes features that are more advanced than those seen in pre-Islamic desert forts. (author's photo). Drawing by Marcus Audens.

Reference:

David Nicolle, Saracen Strongholds AD 630 - 1050. the Middle East and Central Asia, Osprey Pub., Fortress 76, 2008