Sabbath & Sunday as late as 390

But the seventh day is the sabbath of the LORD thy God:

Exodus 20:10

 

"...the 390's: 'The synagogue on Saturday, the church on Sunday'

was a familiar summary in practice. In the 430's, the Council of Laodicea ruled in detail against Christian observance of the Jewish Sabbath."
Pagans & Christians p.482 Robin Lane Fox




As late as nearly 400 AD, many Christians were still keeping Sabbath, some blending with Sunday observance. Reasons included keeping Sunday to distinguish themselves from the Jews in town, the influence as early as the mid 100's of the Bishop of Rome pushing for Sunday as a special day in regards to setting a date for "Easter", the entering of the church in the 300's under Constantine of many pagans who kept Sunday as a holiday (holy day to the venerable Sun) and just out-right apostasy.