In 1910, while Azerbaijan was under Russian occupation, a new French Catholic church was being built in Tabriz. How this happened was the question that foreign diplomats and Iranian authorities were asking. The church belonged to the Congregation of the Mission (Lazarites). The new building surprised everyone, because according to the Qajar Shahs’ orders, the Christians in Iran were not allowed to construct new churches or any other buildings for institutional activities. They were only allowed to repair and restore the existing ones. For the same reason, each Christian group in Iran claimed the ownership of both big and small churches in different cities and towns. Azerbaijan was a meeting point of different competing Christian groups; Iranian Armenians, Chaldeans, Assyrians, Nestorians and Orthodox, as well as Catholic, Protestant and Orthodox missionaries from Britain, France, America and Russia. This new church was built, not in a lesser known village, but in Tabriz, this big key city. The church was not small by any means; rather it was 8 meters high, with a thirty-meter tower and a capacity of 500 people. It is actually the biggest church in Iran. The church was built right under the nose of American Presbyterians and British Anglicans, not to mention the Iranian authorities. The building was ready to use in 1912. This paper seeks to establish the place of this incident in the urban history of Tabriz, under Russian occupation. To do so, it will first discuss the wider geopolitical context of the city in 1906-1912, during the constitutional movements. Using an array of sources, French, Persian and English –from diplomatic and Lazarites’ archives - it will next narrate the procedure of this church’s construction in this crucial context of the city. These are correspondences and reports from the missionaries, French Consuls, British diplomats, Iranian governors and ministers about the story, the problems, frictions or satisfactions, from the time these Catholics tried to buy the land up until the time the church was completed. The main conclusion of this paper is that the presence of the Russian army – whom the Lazarites called their “real alliance” - in Tabriz, on one hand worried the Iranian authorities and prevented them from understanding what was going on, and on the other hand, supplied the “power” the Lazarites needed to build this church.