One of the three tombs built in Maragheh, Gunbad-i Qabud has a decagonal brick chamber with a stone base and a crypt. The entrance to the chamber is on the west side of the structure, while the entry to the crypt is along the base, facing east. The monument was originally built with a double dome, of which only the base of the outer dome remains. The inner dome was probably spherical and the outer dome must have been a polyhedral cone; most tombs in northern Iran and in Azerbaijan have conical roofs. The tomb is often attributed to the Christian mother of Hulagu, the Mongol ruler who conquered Iran in the thirteenth century, though this has been questioned based on the Quranic verses used in the tomb's decoration.
The corners of the decagon are articulated with ten engaged columns on the exterior. Ten pointed arches, one on each façade, spring from the columns at about two thirds of the way towards the cornice. Below the springing of the arches, the surfaces are covered entirely with a brick pattern of interlacing pentagons. Above, the tympanum of each arch is carved with a three-tier muqarnas. The surface of the muqarnas and the arch spandrels are filled with dense labyrinthine patterns rendered in brick and mosaic faience. Above the arches is a band of Quranic inscriptions - verse twenty-six from the second Sura - composed in Kufic style and topped by an intricate muqarnas cornice. Brick ribs are used to outline the arches and the corners of the exterior. Faience has been used to highlight the decorative elements above the spring of the arches, such as the inscriptions carved into the arch soffits. Faience had appeared earlier in Gunbad-i Surkh, another tomb built in Maragheh.
The entrance to the chamber is set within a niche and crowned by an intricately carved muqarnas. The delicate features of the muqarnas have been largely damaged. Above the muqarnas is an inscription, also damaged, that contains the date of the building. Contained within a rectangular frame, the entrance is about 2 meters above ground level.
The interior of the chamber is also decagonal, with deep niches carved into its sides. A pointed arch crowns each niche. The zone of transition to the dome consists of twenty small squinches and a band of inscription in Naskhi style, containing Quranic verses one to five from Sura al-Mulk; these are the major decorative elements of the plastered interior. The crypt has a Greek cross plan and a groin vault. A carved plaster panel on the wall, composed in Naskhi style, contains verse (26 and 27) from Sura ar-Rahman.
The similarities between this tomb and the Tomb of Mu'mina Khatun located in Nakhchivan, two hundred kilometers to the north of Maragheh, are noteworthy. The two towers not only have identical plans, but their major decorative features are also similar. The Tomb of Mu'mina Khatun, built in 1186 A. D., is one of the earliest monuments where faience was used as an exterior decorative element. Gunbad-i Qabud represents a later and more developed stage in craftsmanship.
In an old photograph a second entry is visible. However, since no decorative features are used to adorn it, this doorway could not have been part of the tomb's original conception. This entrance is seen blocked in later photographs.
Daneshvari, Abbas. "A Stylistic and Iconographic Study of the Persian Tomb Towers of the Seljuk Period." Ph.D. Diss., The University of California, 1977.