That looks too large and too prominent to have been buried and forgotten, sitting as it does on a bluff overlooking the river. This is a part of the world with ruins everywhere. Is this a case of something that was known but unidentified, but enough digging has now been done to contextualize and date it?
Possibly isolated, probably just blended into the landscape, give or take sands blowing in. Also, the whole country is so lousy with ruins, and the local gentry have been woefully uninformed of the origin of most or all of them since Greek times at least.