Tower Tombs at Shir/Jaylah.
From my files: I made several visits after hearing reports by locals describing towers & later reports from a helicopter pilot who noted these strange towers while flying over the area.
See link below for a very detailed and interesting report by: Paul Yule and Gerd Weisgerber on these and other tombs in Oman. Well worth a read.
Link: Tombs in Oman.