The Friday Mosque of Gulpayigan was built by Seljuk Sultan Muhammad Tapar I (1105-1118), son of Malik Shah I. Only the dome chamber remains from the Seljuk period mosque, which was integrated into a monumental four-iwan mosque during the Qajar period. 

In "L'Art de l'Iran" (1962), André Godard lists the Golpayegan mosque as an example of a "kiosk-mosque", which he considered to be the continuation of Sasanian temple typology under Islam. Consisting only of a chahar taq style dome chamber and a free-standing minaret, this type of mosque would accommodate praying crowds in a walled courtyard around the sanctuary. Writing three decades later, Bernard O'Kane, cautiously rejects this hypothesis and argues instead for the prevalence of Central Islamic plan types in early Iranian mosques, where a roofed hypostyle hall with wooden columns would surround the dome chamber. The latter hypothesis may be considered to hold given Ghulam Ali Hatim's reference to Seljuk columns recently unearthed at the northeast side of the courtyard while excavating for a new addition.

Built in the nineteenth century, the Qajar period mosque is roughly rectangular in plan and consists of vaulted and domed prayer halls enveloping the four sides of a rectangular courtyard. It is oriented northeast-southwest and measures about seventy-three meters by forty-four meters on the exterior. Measuring twenty-six meters wide and thirty-two meters deep, the courtyard is symmetrically arranged with two grand square iwans to the northeast and southwest, and two small iwans to the northwest and southeast. The main portal opens into the northeast iwan, while secondary portals lead into the courtyard through the northwest and southeast iwans. The grand southwestern iwan is sheltered by a dome and leads directly into the equally large sanctuary -- the Seljuk dome chamber--, which has a mihrab niche on its qibla wall. 

The square dome chamber, or sanctuary, is constructed entirely of brick and is opened on three sides with vaulted archways flanked by embedded columns. The east and north corners of the chamber have thick double columns marking the corner, flanked by narrow archways cut into the adjoining walls that are topped by arched windows. Only a single such archway exists at the western corner and there are none at the southern corner. Above, the transition to the shallow brick dome is achieved with muqarnas squinches built into the corners of the tall octagonal drum. Light comes in through four honeycomb windows pierced into the dome's base, which is ringed with a band of Kufic inscriptions.

Centered on the qibla wall, the three-sided mihrab niche of the Seljuk dome chamber has a stucco muqarnas hood, topped by a blind arch carved with inscriptions, and an inscriptive plaque. Three bands of Kufic inscriptions separated with bands of geometric motifs border the mihrab. A shallow niche with a cusped arch forms a smaller mihrab to the left of the main niche and is marked with a Kufic inscriptive plaque and frame of Kufic inscriptions. The place of the minbar to the right of the main mihrab is occupied by an unmarked niche with a cusped arch. The interior surfaces are adorned with brick panels with intricate geometric motifs and geometric compositions of the God's name in Kufic letters and have traces of tiles that were used to highlight the patterns. The exterior of the dome structure is left plain, with the exception of a ring of large diamonds encircling the dome's base.

The single minaret of the mosque is located outside the precinct, behind the qibla wall and also dates from the Seljuk period. Its octagonal base is joined by a tall cylindrical shaft, which is topped by a narrow turret placed off-center. The base is carved with shallow niches on each side. Simple brick patterns adorn the shaft, which displays remnants of turquoise tiles at the top.

Sources:

Godard, André. The Art of Iran, 279. New York: Frederick A. Praeger Publishers, 1965.

Hatim, Ghulam Ali. Mimari-i Islami-i Iran dar Dawrah-i Saljuqian, 39. Tehran: Mu'assasah-i Intisharat-i Jihad-i Danishgahi, 2000.

O'Kane, Bernard. "Iran and the Central Asia". In The Mosque: History, Architecture, Development and Regional Diversity, 118-139. Edited by M. Frishman and H. Khan. New York: Thames and Hudson, 1994.

Pope, Arthur Upham, ed., Phyllis Ackerman, assist. ed. A Survey of Persian Art from Prehistoric Times to the Present. Vol. 3, Architecture, Its Ornament, City Plans, Gardens, 3rd ed., 1014. Tehran: Soroush Press, 1977.