Ante-Nicene Fathers Volume 5
Cyprian: Epistle LXXIV
As the editor's introduction says, "The argument of this letter is exactly the same as that of the previous one, but written with a little more vehemence and acerbity than becomes a bishop..." We can add "and with a little more length as well," because this epistle is long by ancient standards.
Again, Cyprian is concerned with the unity and purity of the church, and again this involves a questionable view of church polity that lays groundwork for openly bad theology. But, because there's really nothing new in this Epistle, it can be skimmed. Do be sure to read at least the first three paragraphs, though--there's some good stuff on unity in God to be found, and paragraph 10, where we get some persecution narrative and weirdness with demons and women baptizing... Likewise paragraphs 17 and 24 show Cyprian telling us exactly how NOT supreme the pastor of Rome is relative to other churches and pastors.