The date of construction for the two towers at Kharraqan, commonly referred to as the East and the West towers, are respectively 1067-8 and 1093. The inscriptions on the towers identify the architects as Muhammad ibn Makki al-Zanjani and Abu'l-Ma'ali ibn Makki al-Zanjani in the later tower, who is probably the former's son or brother.
Both towers have octagonal chambers with engaged pilasters at every corner. Each of the eight facades of the two towers is adorned with a decorative panel. Each tower is made of thick brick walls onto which the decorative brick panels have been attached. The east tower has a north-east facing entrance while the West tower's entrance is to the north. Two of the buttresses at the eastern tower contain spiraling staircases within them. This is different at the Western tower where only one buttresses contains a staircase. Both tombs were built with double domes; the exterior domes have not survived. This is one of the earliest, if not the earliest, applications of a double dome in a tomb tower. The tradition of a double dome had existed before in Islam, such as in the conical roof of the Gunbad-i Qabus.
The common feature of the panels in both towers is a decorative niche flanked by a pair of slender columns. Framed by the corner buttresses, these panels are minor variations of the same decorative theme. In the west tower, the panel within the niche has been divided into two parts by three small, slightly protruding, arched niches. The top and the bottom parts of the panel have been decorated differently with varying weave patterns. In the east tower, built first, these panels have been left uninterrupted and only include one pattern per panel.
All panels are distinguished by a different decorative pattern but are unified in their use of a brick unit as the primary constructive element. The brickwork, recalling the earlier tomb of Ismail the Samanid built in the 10th century in Bukhara, is a complex and varied series of patterns. It is identified by deeply recessed mortar joints and includes a wide variety of patterns including star and polygonal shapes. Also, common in both towers, is a line of Kufic inscriptions in Arabic that run the entire perimeter of the buildings above the arches, interrupted only by the corner pilasters. On the Eastern tower the writing has been identified as the last three verses of the Koranic Sura 59.
The interior, also octagonal, is covered with plaster. Inside the chamber of the eastern tower can be found illustrations that are among some of the most well preserved examples of early Saljuq mural painting. One of the illustrations, framed by a keel shaped arch on the lower side of the interior walls, is a depiction of a mosque lamp hanging with three chains and is inscribed in Kufic: "Blessing to its owner". The other illustration is a stylized design of birds sitting in the branches of a pomegranate tree.
The bases of the towers have suffered great damage due to the rising water table and have only informally been repaired by the local people. The western tower, having had the structural advantage given to it by the elimination of a second stair inside its buttress, has survived more intact.
Sources:
Hoag, John D. Islamic architecture. Milano: Electa Architecture; [S.l.]: Distributed by Phaidon Press, 2004, c. 1973.
Stronach, David and T. Cuyler Young Jr. "Three Seljuq Tomb Towers." Iran, 1-20. London: The British Institute of Persian Studies vol. IV, 1966.
Hatim, Ghulam Ali. Mimari-i Islami-i Iran dar dawrah-i Saljuqian. Tehran: Muassasah-i Intisharat-i Jihad-i Danishgahi, 2000.