The ruin of Ribat-i Mahi has long been identified as an important site of the Middle Islamic period in Khurasan. Its position on the caravan route between Mashhad (Tus) and Marv fits with the development of long-distance relations between the Abbasid and the Timurid period. During the Saljuq period, this route saw major building activities, of which the caravanserai of Ribat-i Sharaf and the gateway of Do Barar are important remains. Ribat-i Mahi also figures in the secondary literature on Islamic architecture. It is frequently dated to the early 5th/11th century, on the basis of an episode transmitted by the 9th/15th century author Hafiz-i Abru. However, a stylistic comparison with Ribat-i Sharaf and with buildings in Marv (Turkmenistan) demonstrates that the extant ruin should be attributed to the Saljuq period. This dating receives new support from a photograph held in the Gulistan Palace archive. The picture, dated 1311/1893-94, shows the gate of Ribat-i Mahi with an inscription that has now vanished. In the text, the name of Sanjar b. Malikshah can clearly be identified. Parts of his royal titulature are subject to discussion, as well as the name of another person, who is probably to be identified with the vizier Sadr al-Din Muhammad b. Fakhr al-Mulk b. Nizam al-Mulk. From his biographical dates as they appear in written sources, the construction of Ribat-i Mahi would most likely to be dated between 500/1106-07 and 511/1117-18.