Gonbad-e Jabaliyeh, also known as the Gabri Dome (also Jabel-I Sang)
Located in a cemetery that was once home to many tower tombs East of the Maydan-e Arg is the Gonbad-e Jabaliyeh, one of the earliest surviving tombs with a double dome to be found in Iran.
This stone and brick domed building is something of a puzzle to historians. The consensus is that it certainly predates the Seljuk period, but its origins may go back to the Sassanian period or even earlier.
A number of suggestions have been made as to its function, including as an observatory, but it bears a similarity to other tomb towers. It is remarkable though, for the fact that it is made of stone rather than baked brick. The double dome that you see now is a later addition and is made of brick. The ground plan is octagonal, and the building is interesting because it allows you to see, both inside and out, a transition from octagon to dome.
Restored many times, as this photograph of a century ago shows, the niches and arches, which would have helped with load-bearing as well as being decorative, would always have been an important feature of the building.
The Gonbad is now a museum, home to many stele, grave-markers and other worked stone from the local area.