Farming – Wadi Al Hoqain.
Date palms, sugar cane, the henna plant, along with animal fodder; all grown in this wadi, renowned for its abundance of water all year round.
There has been some form of settlement here from as early as the bronze age, maybe even earlier.
I have not been able to find any history about the fort, although commanding such a prominent place, it does surprises me that it doesn’t get mentioned – I’ve probably not looked hard enough. 🙂
Working my way through the book shown below, so with luck.
The countries and tribes of the Persian Gulf
By: Samuel Barrett Miles Pub. 1919.
David A Lockwood 
Interesting how the same place is inhabited -usually by different peoples- throughout the ages. Sometimes a town or a village is burned down by enemies and uninhabited for hundreds of years; and then some new settlers take the same place, for different reasons: proximity of water, good soil, closeness to ancient roads, or maybe a good natural defense. Strange however.
You’re right, I have seen it a lot in Oman. Grave sites are another example; reusing the same tombs or site, two or three times over hundreds of years.
I think this happens almost everywhere in the world. Maybe on a larger scale there, in the harsh desert climate, with limited resources.