The Didache is one of the earliest non Biblical writings that gives us some insight to how the early Christians worshiped. It has an early example of the Liturgical Mass. It is essentially the same form of Eucharistic Liturgy as the Mass has today. Note also that it is considered a sacrifice just as it is today.
“1. But every Lord’s day do ye gather yourselves together, and break bread, and give thanksgiving after having confessed your transgressions, that your sacrifice may be pure. 2. But let no one that is at variance with his fellow come together with you, until they be reconciled, that your sacrifice may not be profaned. 3. For this is that which was spoken by the Lord: In every place and time offer to me a pure sacrifice; for I am a great King, says the Lord, and my name is wonderful among the nations.”
See the full Didache here:
