The Gate diagram of Ukhaydir, Umayyad, Iraq

Qala'at Rustaq, Early Islamic Oman

The 'later tower' means that sometime since the fortification was 

constructed, a tower was added  to the curtain wall.  It was

 well known that as european forces came into contact with 

muslim forces at a fortification, the Muslim engineers, borrowed 

the technology that they saw in the improvements of their 

opponent's fortifications . 

Muslim State at the Death of Muhammad in 632 CE

Reference:

D. Nicolle, et al, "Armies of the Muslim Conquest," Men-At-Arms 225, Osprey, 1993, P. 4

"Ship's Prow Tortoise" #7

This view of the machine shows it right side up.  Note the two iron plates for shunting aside any flamable material or logs used against the machine In the top vee of the angle one can see the hinge assembly for the main brace timber.

"Ship's Prow Tortoise" #6

This view of the tortoise shows the machine upside down, showing the wheels, axles and crossbrace.

"Ship's Prow Tortoise" #5

The hieght of the two wings from the ground was about seven feet, which was enough to protect the workers behind the tortoise wings.

"Ship's Prow Tortoise" #4