"Lectures on the history of the Ancient Church, first volume. Introduction to church history" by Vasily Bolotov, a great Orthodox historian who knew how to combine scientific objectivity, fidelity to Tradition and a philosophical gift. In history, Bolotov saw “the voice of the church, scattered not only in space, but also in time, an irreplaceable voice that has always and everywhere been an object of faith for everyone.” Bolotov's "Lectures on the History of the Ancient Church" is a brilliant work, a classic of church historiography, perhaps the best on its topic (although a century has passed since their reading). "Lectures on the history of the Ancient Church. Introduction to church history"  contains the necessary information to begin studying church history: preliminary concepts. auxiliary sciences, sources, historiography.