This paper examines pious endowments (waqfs) established along the Danube by the Chief Eunuchs of the Ottoman imperial harem. Although they were technically personal endowments, all were connected to the pious foundations for the Muslim holy cities of Mecca and Medina, of which the Chief Eunuch was superintendent. All these foundations consisted of religio-educational institutions funded by commercial operations. They date to the very first Chief Harem Eunuch, Habeshi Mehmed Agha (term 1574-91), who founded an entire town, known as Ismail Geçidi (Ismail’s Crossing) in the Danube delta in what is now Ukraine, where the Danube flows into the Black Sea. Roughly 120 years later, his successor el-Hajj Beshir Agha (term 1717-46) encompassed most of the Danube delta in an endowment that provided for a fortified lighthouse with a local garrison at the delta’s easternmost point, in Sünne (today Sulina), Romania, to guide ships entering the Black Sea from the Danube with grain for the imperial capital. The endowment deed also provides for grain warehouses, a coffeehouse, and a shop selling sheep trotters. Farther inland, el-Hajj Beshir founded a madrasa at Sistova (today Shvishtov), on the Danube in what is now Bulgaria. This institution, also supported by a coffeehouse and a sheep trotter establishment, included a library stocked with seminal works of Hanafi jurisprudence. In a town far away from the imperial capital, and even from the provincial capital Sofia, the majority of whose inhabitants were Orthodox Christians, this madrasa must have represented a vital link to the official Ottoman religious establishment, while its library provided a critical infusion of Hanafi texts. This is consistent with el-Hajj Beshir’s religious foundations elsewhere in the empire, including Cairo, Medina, and Istanbul itself, but in a frontier region, it gained added importance. These foundations clearly did not exist in isolation from each other. El-Hajj Beshir Agha was aware of Habeshi Mehmed’s foundations. The foundation deed for his endowment at Sünne even provides for funds for Ismail Geçidi, thus demonstrating that waqf could be used to supplement pre-existing foundations. Collectively, these pious foundations emphasized the Ottoman presence in the Danube, a critical frontier region facing the enemy Habsburgs to the northwest and the enemy Russians to the northeast. In addition, they shored up state-sponsored Sunni Islam of the Hanafi legal rite, providing local Muslims, surrounded by Christians and far from the imperial and provincial capitals, with the foundations of legal and theological education.