Library Eusebius of Caesarea Church History
Book 2
Chapter 16: Mark first proclaimed Christianity to the Inhabitants of Egypt
1. And they say that this Mark was the first that was sent to Egypt, and that he proclaimed the Gospel which he had written, and first established churches in Alexandria.
2. And the multitude of believers, both men and women, that were collected there at the very outset, and lived lives of the most philosophical and excessive asceticism, was so great, that Philo thought it worth while to describe their pursuits, their meetings, their entertainments, and their whole manner of life.
English translation by Arthur Cushman McGiffert, in Nicene and Post-Nicene Fathers, Series II, Vol. I (eds. Philip Schaff and Henry Wace; Buffalo: Christian Literature Publishing Co., 1890). Public domain. Digital text via New Advent Church Fathers.