My twitter friends helped compile this list. We talk about the church fathers and mothers, the desert fathers, the early martyrs. This list is books by them or about them. Some of the books go beyond early church days into history. Take your pick:

How Christianity Saved Civilization (Mike Aquilina, James L. Papandrea)

The Early Church - The Penguin History of the Church (Henry Chadwick)

When the Church was Young (Marcellino D'Ambrosio)

The History of the Church: From Christ to Constantine - Penguin Classics (Eusebius)

Book of Martyrs - Pure Gold Classics (John Foxe)

The First Crusade (Peter Frankopan)

The Story of Christianity (Justo Gonzalez)

The Story of the Copts (Iris Habib El Masri)

Christianity: The First Three Thousand Years (Diarmuid McCullough)

The Path of Christianity: The First Thousand Years (John Anthony McGuckin)

Jesus Through the Centuries (Jaroslav Pelikan)

Mary Through the Centuries (Jaroslav Pelikan)  

For Our Salvation: Two Approaches to the Work of Christ (Geoffrey Wainwright)

The Sayings Of the Desert Fathers: The Alphabetical Collection (Benedicta Ward, Metropolitan Anthony) 

The Orthodox Church (Timothy Ware)

The First Thousand Years (Robert Louis Wilken)

Where God Happens (Rowan Williams)