The seventh recorded worldwide record in Iran, dated July 24, 2005 It has been registered as UNESCO World Heritage Site. Soltanieh was originally used as a hunting ground used by the Irish rulers, and later they decided to build a city in this place. The construction of this citadel began on behalf of Arghon Khan and Ghazan Khan and ended with Oljito. With the construction of the royal citadel and Soltanieh dome since 703 AH Until the year 713 AH, the capital was transferred from Tabriz to Soltanieh, and its first Islamic religion came to be named Sultan Muhammad Khodabandeh. The Royal Citadel, also known as the Old Fort, was built with a square plan of 314 × 296 meters and a width of 3 meters, with 16 towers and two northern and southern gates, using green limestone. The northern gateway of the ceremonial gate and its southern gate has been dedicated. The average height of the citadel is 4 meters and the perimeter of the citadel has been dug with a width of 30 to 40 meters. The city of Soltaniyeh, which was selected as the capital of Ojjitou after his death, fell out of boom. Soltanieh Dome is built inside the royal citadel. This three-story building consists of three sections: dome-house, Torbat-e-yard and chapel. The most important part of the citadel is Soltanieh Dome, where the tomb of Sultan Mohammad Khodabandeh is also inside. The blue dome has a height of 48.5 meters and an inner crest diameter of 25.5 meters, located on an octagon with a length of 17 meters each side. The main materials used in this building are brick. The invention of the dome of the two continuous shells was first made in the history of Iranian architecture in this building. The outer shell of the dome is covered with turquoise tiles. In this building, tiling, plaster painting, grinding bricks, gypsum and brickwork and plaster on the fabric, inscriptions with the themes of Quranic verses and hadiths as decorations have been used. This dome has 8 mujenah which is located around the dome to bring the prayers of Azan to all parts of the city. Of course, this part of the building has been demolished. All the walls of the dome have inscriptions which are covered with Quranic verses and the name of Imams. The minaret is located in an octagonal dome. The tombstone is located on the southern side, measuring 17 x 8 m. The other part of this building is a chapel located on the south side of the building and under the Torbat House. Making an octagon is one of its mysteries. Because eight are not one of the special numbers like 7 and its use is either due to the strength of the building or the building is like a sunny clock to find the right time, which, of course, requires more research. In any case, this building is one of the most interesting examples of the Ilkhani era in Iran. Soltanieh dome has been restored several times during Safavid and Qajar dynasties. Soltanieh dome is about the height of the Santa Maria Florence Italy (86) meters and the Aesophia mosque of Istanbul (56) meters is the third highest dome in the world. This dome, as one of the most prominent examples of the architecture of the city, has had a significant impact on the architecture of the world's monuments, and one can clearly see this effect in the architecture of the Church of Santamaria Delphiore (Mari Moghadas) in Florence, which was built 100 years after the construction of Soltanieh Dome . The citadel was destroyed by the attack of Timur Gurkani, but he kept his tomb safe for the sultan Mohammad Khodabandeh.