Early Church Liturgy
The Didache
The Didache was written some time in the first or the second centuries AD. It includes a couple chapters on the Divine Service as it existed at that time.
Justin Martyr
The First Apology of Justin Martyr was written circa 155-157. St. Justin addresses the Early Church’s Divine Service in three chapters:
The Apostolic Constitutions
The Apostolic Constitutions were written circa 375-380. They have a series of “books” (6-11) that deal with liturgical matters: