It is the Mausoleum of Oljaytu which was constructed during 1302–12 CE in Soltanieh.
Soltanieh was the third capital of the Ilkhanid dynasty (after Maragheh and Tabriz), founded by the Mongols. Since the area had horse-riding site and greenery, it was located along the Silk Road.
Soltanieh Dome was constructed in 10 years. Its construction included two eras: One included brick and tile while the other included plasterworks.
On the sides of the ceiling, Qur'anic verses and attributes of God have been written in beautiful scripts—symbolizing both the Iranian art and the submission of Iranians to the last divine religion.
The dome is 48.5 meters in height and 25.5 meters in diameter.
The length of each side at 17 meters. It has eight doors and eight porticos. It includes three storeys and comprises three sections: Dome, cellar and tomb."
Soltan Mohammad Khodabandeh has been buried somewhere in cellar. Since Mongols were afraid of the exhumation, they kept the burial place a secret. The tomb house is located on top of the cellar.
The Ilkhanids had converted to Shia religion, and they are believed to have wanted to transfer the relics of Imam Ali (PBUH) from Baghdad to Soltanieh. This never happened and the shrine became the mausoleum of Oljaytu instead. The soil of Karbala and Najaf has been used in the tomb house to improve the spirituality.
Lots of houses were purchased and their lands were added to the precincts of Soltanieh Dome.
Soltanieh Dome is the largest brick dome worldwide. The building's foundation is 0.5 meter. But it should be at least 2.5 meters. However, it can bear the weight because of its octagonal shape, Iran Daily wrote.
Also, eight minarets help the building maintain the balance. In addition, the building has been buttressed by many scaffolds installed within it.
Soltanieh Dome has witnessed and resisted 33 earthquakes — 1990 Manjil-Roudbar earthquake was the biggest one.
After the death of Oljaytu in 1316 CE, the city went into oblivion. Later, it fell into the hands of minor dynasties.
In 1384 CE, Tamerlane's army seized the city and sacked it, but spared Oljaytu's mausoleum. In the following years, the city suffered, though it continued to function as a commercial center comparable to Tabriz. In the 16th and 17th centuries CE, Soltanieh gradually declined and remained in ruins. Only a village was built over the remains. Oljaytu's Mausoleum underwent some renovations in the 19th century CE. At the same time, the plain served as an instruction camp for the army of Qajar kings.
Soltanieh is one of the outstanding examples of Persian architecture and a key monument in the development of Islamic architecture. The octagonal building is covered in turquoise-blue faience. It is the earliest example of the double-shelled dome which still exists in Iran. The mausoleum's interior decoration is also outstanding.
Arghun Khan, the fourth Mongol ruler in Persia, decided to build a summer residence in this region, because it boasted good hunting grounds and rich pastures for horse breeding. His son, Ghazan Khan, had a mausoleum built over his tomb, known as Noor Hill.
There is little information about the start of the new settlement until Oljaytu (later Soltan Mohammad Khodabandeh) came to power in 1304 CE when he decided to expand the city and make it his capital, naming it Soltanieh.
Together with Tabriz, Soltanieh became a major trading center on the route linking Asia and Europe.
Structurally, the building is considered a masterpiece. The interior walls were originally decorated with light golden-toned bricks and dark blue faience tiles. Later, it was redecorated with plaster by using fine ornaments.
The immediate surroundings of the mausoleum consist of a stone terrace in citadel form. Today, it is an archeological site.
The Mongols founded Ilkhanid Empire in Iran with the capital in Tabriz, in the northwest. The title 'Ilkhan' indicated subordinate or peaceful khan in deference to the Great Khan in China. After Kublai Khan died in 1294 CE, the Ilkhanids converted to Islam and the links with China became weaker. The Ilkhanid dynasty governed Iran until 1335 CE.
The dome is the largest in the world after Santa Maria and Hagia Sophia. The structure is made of a mixture of gypsum and to a lesser proportion limestone.
Soltanieh Dome is erected in three floors. The ground floor consists of eight sections. The first floor comprises of halls that run throughout this floor. On the third floor is the foundation column of the dome and the octagonal pillars supporting the minarets.
The entrance to the cellar is from the southern portico. The layout or plan of this cellar is a complex one, consisting of seven segregated sections, each part independent of the other.
The main elements of the artistic effects revealed in Soltanieh Dome are the inlaid brickwork, plaster moldings, engravings and tileworks. All these create harmony that is of great artistic value.