After Tehran was chosen as the capital, the supply of water was one of the necessary measures to be taken as the population increased. In addition to building new qanats, other solutions such as transferring water from the rivers descending the Alborz Mountains could supply the city with drinking water. The maps studied in this research document this engineering action, i.e., to convey water by building a canal from the Karaj River to the city of Tehran. The colored maps are preserved in the Golestan Palace and the Ministry of Foreign Affairs. They contain information about how the canal was built, but with no title, date, cartographer, or exact location. The research question is, what historical and engineering facts can be drawn by rereading the maps, and what other historical architectural and urban achievements do these documents show? The research method employed is descriptive-historical, because the emphasis is on a historical document and narrating an event in the past (Qajar period). This study is also document research because reviewing a visual document is the basis of the research work. This research aims to reread the map as a document in engineering history and to shed light on a chapter of Tehran’s history during the Qajar period. The results show that due to a decrease in water supply, the repair of the canal was on the agenda. Plans for the restoration of the Karaj canal around 1267 AH were most probably made by one of the engineers of the Qajar court, in the early years of Nasser al-Din Shah’s reign, under the ministry of Amir Kabir. The project, however, was initiated by the order of Mohammad Shah, under the ministry of Haj Mirza Aqassi.
