Having set the scenery..I hope... It is now time to look at some of the Omani Forts in detail and I first chose Nizwa Fort.This is an interesting fortification being at the centre of the capital of the interior and on top of its own water supply...with as its main defence a gigantic round tower also acting as a dungeon. This enormous roundel gives it automatic all round defence and superb fields of fire and observation. It is reinforced not only to enable cannon to fire from its walls but also so that it can absorb fire .
I have no evidence that cannon fired at or from the Fort however the weapon at one side of the gate below is apparently Portuguese ...Whereas some cannon were deployed from positions just outside the fort proper e.g. Barka they were on a secondary wall usually tri angular and massively built and able to retreat into the fort in the advent of a too powerful assault and fire from their secondary positions.
Nizwa Fort is examined at
https://en.wikipedia.org/wiki/Nizwa_Fort
Below is the pictorial...Please note that two cannon are displayed outside the door... The one on your left is Portuguese whilst on your right is an 18th C Swedish Iron "Finbanker" on a repro British carriage; Interesting that Finspang in Sweden made these mainly for export and purchased by the Dutch and Portuguese may have been captured by the British in Indian Ocean waters and sold to Oman....It was an 18 pounder.