The connection of the Dominical day (Sunday) with the celebration of the Eucharist can be demonstrated from the very beginnings of Christianity. This study contains a short exposition and commentary on five texts: 'breaking of bread' in Troas according to Acts 20.7, texts on the Eucharist in the Didache, the report of Pliny the Younger about Christians in Bythinia in his letter to Trajan, the description of the Sunday synaxis in Justin's Apology (67.3-5), the report about martyrs from the town of Abitene in AD 304.