Gonbad-e Qâbûs (Tomb Tower of Qâbûs ibn Vashmgîr) on an artificial hill
To build such a high tower, it might have been necessary to make a huge stable
foundation. After the completion of the tower, it is considered
to have been covered with soil and plants as a hill.

There was no town around the mausoleum of Qabus in the 19th century,
though the city of old Gorgan was 3km southeast of it in the 14th century,
but was throughly destroyed by the Mongol army, and transferred
to the current location, 90km west. (photo from a web site)