The Ante-Nicean period had about 7 regions of The Faith that seemed to operate independently of each other.  They were...  

1. EUROPE - Latin speaking Western Europe - which grew into the Catholic Church. 
2. EUROPE - Greek speaking Eastern Europe - which grew into the Orthodox Church. Closely aligned with Catholics for many years, but still differing with them on many thoughts from as far back as writings indicate.
3. AFRICA - Greek speaking North Africa.  They tended to agree with the Latin church on some points but the Greek Eastern Europe on many others.
4. AFRICA - Deep Africa
5. ASIA - Aramaic speaking Mid-East
6. ASIA - Far East/Asia - Also Aramaic speaking, but a different dialect of Aramaic.
7. Nazarenes - The ancient name for Messianic Jews or Jewish believers in the Messiah.

  Most of these regions were celebrating the original (real) Sabbath until Constantine, but Constantine did not originate Sunday keeping - he only expanded it.  Their practices varies, as is explained by this account from early history:

"But that they who are at Rome do not observe those things in all cases which are handed down from the beginning, and vainly pretend the authority of the apostles;… and that all things are not observed among them alike, which are observed at Jerusalem, just as in very many other provinces also many things are varied because of the difference of the places and names....
But with respect to the refutation of custom which they seem to oppose to the truth, who is so foolish as to prefer custom to truth … And this indeed you Africans ...that when you knew the truth you forsook the error of custom. But we join custom to truth, and to the Romans' custom we oppose custom, but the custom of truth; holding from the beginning that which was delivered by Christ and the apostles..." (Cyprian, Epistle LXXIV, §§ 6, 19)"

The historian Socrates Scholasticus (379-450 AD) tells us that in ancient times, there were only two cities where Christians celebrated Sunday as a day of worship; every other region of the world they celebrated on the Sabbath as it was understood by Judaism. Socrates wrote...

"For although almost all Churches throughout the world celebrate the sacred mysteries on the Sabbath every week, yet the Christians of Alexandria and Rome, on account of some ancient tradition, refuse to do this." (Ecclesiastical History, Socrates, Bk 5, Ch.22, pg 289)

Socrates can be considered an unbiased source on this, since he spoke against the need for Christians to obey the Mosaic Law in this same chapter. Writers from each of these various regions also tend to support these claims. Of the two cities where Socrates said Sunday was celebrated, we have...

• The Roman Justin Martyr (c 150 AD) confirms that believers in Rome celebrated Sunday.
• He taught that Christians celebrated Sunday in Chapter LXVII of his First Apology (click here to read).
•   Justin was born in Samaria and believed to have moved to Rome, so his perspective was a Roman one.
• And from Alexandria, we have the words of Barnabas (c 150 AD) also taught that it was customary to meet on Sundays, even teaching a "replacement theory" on this in his letter.
•   His letter originated from some Greek speaking source, and most likely Alexandria according to many scholars.

But every other source we have on this topic from regions outside Rome and Alexandria talk about celebrating the 7th day Sabbath (Friday night to Saturday night). Even places very near to Rome such as Spain and Milan celebrated the Sabbath. We see this in...

"For in the Church of Millaine (Milan), it seemes that Saturday was held in a farre esteeme... Not that the Easterne Churches, or any of the rest which observed that day were inclined to Judaism; but that they came together on the Sabbath day, to worship Jesus Christ the Lord of the Sabbath." (History of the Sabbath, Dr. Peter Heylyn, London 1636, Part 2, para. 5, pgs 73-74)  

While Rome celebrated Sunday, we know nearby Spain kept the original Sabbath on Saturday, because the canon 26 of the Council of Elvira (c.305 A.D) , Rome introduced fasting on the Sabbath to counter Sabbath keeping that was occuring in Spain.

In other regions....

Far East

Christians in Persia kept the Sabbath, even into the mid-4th century. Here's a quote from the time of Shapur II (335 to 375 AD) from a follower of Zoroastria:

"They despise our SUN-GOD. Did not Zoroaster (Prophet of Mithra, the sun-god), the sainted founder of our divine beliefs, institute Sunday one thousand years ago in honour of the sun and supplant the Sabbath of the Old Testament. Yet these Christians have divine services on Saturday." (The Syriac Church and Fathers, by O'Leary, pg 83-84)   

Zoroaster is believed to have lived circa 628 B.C.-c.551 B.C. This lends insight into several issues. One, is that believers in Persia celebrated the Sabbath, not Sunday. Also, that pagan sun-god worship was celebrating Sunday as a day of rest/worship several hundred years before Messiah. It was for this reason that the day was named "SUN-day" - in honor of the Sun-god many pagans worshiped. Just like Monday was named for the Moon goddess.

In the Orient...

"The ancient Christians were very careful in the observation of Saturday, or the seventh day...It is plain that all the Oriental churches, and the greatest part of the world, observed the Sabbath as a festival...Athanasius (A.D. 297-373, Bishop of Alexandria) likewise tells us that they held religious assemblies on the Sabbath, not because they were infected with Judaism, but to worship Jesus, the Lord of the Sabbath. Epiphanius says the same." (Antiquities of the Christian Church, Vol. II, Bk.xx, Ch.3, Sec 1, 66. 1136,1137)   

Athanasius also says in his original writing that they did not hold the Sabbath to be holy - just that they kept that day.

Lloyd (The Creed of Half Japan, p23) says that in 220 AD,  the Kushan Dynasty of North India called a council of Buddhist priests at Vaisalia to deal with the issue of Buddhist monks who were observing the Sabbath after studying the Bible.

Africa

There is evidence that North Africa observed the Sabbath according to the Oxyrhynchus Papyrus (c. 200-250 A.D.) (Pt. 1, pg 3, Logion 2, verses 4-11, London: Offices of the Egyptian Exploration Fund, 1898)   

Origen (185-254 AD), who was from North Africa, also promoted Sabbath keeping according to the original Mosaic Sabbath. (Homily on Numbers 23, para. 4, in Migne, Patrologia Groeca) This is in spite of the fact that Origen taught Replacement Theology and blamed the Jewish race for killing the Messiah and even in spite fo the fact that he was so influenced by the church in Alexandria. Of course, Origin had a larger world view, having been school in Caesarea (See the Note to Gregory Thaumaturgus )

And it is well known that in Deep Africa, this is STILL the tradition to this day, among those congregations that trace their legacy to apostolic origins (rather than missionary plants).

One writing indicating Socrates MAY have missed one. Rome, Alexandria, and Antioch were all three closely aligned in the early centuries of the faith. Alexandria was very much the center of the Greek pseaking world - certainly of Greek speaking North Africa. Antioch was on the crossroads of the Greek speaking Eastern Europe and Aramaic speaking Asia / MidEast. Ignatius of Antioch, c 150AD, mentions that Sunday worship was the rule there. So perhaps Socrates never visited Antioch. Or perhaps Antioch had changed to follow the custom of the cities around her, which observed Saturday, between the 100 or so years from the time of Ignatius to the time of Socrates.

But when we put all these writings together, we see they basically agree with Socrates - that only a small handfull of cities in the Ante-Nicean period celebrated Sunday as a day of worship and everywhere else it was the original Sabbath that was celebrated - with Antioch being the one possible exception that Socrates' observation might have missed.

So What Happened? - The Evolution of a Drift to Sunday Worship

The earliest observers of Sunday worship in Rome and Alexandria propbably observed this day because most of the society around them did so. Sunday keeping by pagan sun-god worshippers is known to exist as far back as the days of Zoroaster (c.628 B.C.-c.551 B.C), in that he is given credit for having established Sunday as the day they honored the sun god.

In canon 26 of the Council of Elvira (c.305 A.D) Rome began advocating fasting on the Sabbath to counteract Sabbath keeping it cited as occuring in Spain at the time. Subsequent Popes also upheld this edict. This would run counter to Jewish tradition, which forbids fasting on the Sabbath, seeing eating as a part of "resting".

About 20 years after Elvira, the Catholic Church got some help from Constantine when he required Christians to take the following oath upon conversion to the faith...

Then, in 366 AD, Rome condemned via a curse anyone obeying the 4th commandment.  The Council of Laodicea (c.366), Canon 29 says ...

"Anathema" means "cursed" or "condemned" Is this the spirit/attitude of someone acting in obedience to God?  Cursing someone for resting on the Sabbath??? But eventually, Rome got its way and influenced most of the Christian world around them to switch to celebrating on Sunday, rather than Friday night / Saturday day.

This final effort by the Laodicean council seems to have finished the effort, since many writers from around this time period name the Laodicean Council as the event that put an end to Sabbath keeping by the Christian Church.

What does the Bible Say?

No where does it say the Sabbath was moved from Saturday to Sunday. In fact, much circular logic has to be used to support the idea that scripture teaches this. Because each of the gospels tell us Y'shua (Jesus) rose on the day after the Sabbath and on the first day of the week, thus the gospels attest to the idea that the Sabbath is the 7th day. Furthermore, since the gospels were written AFTER Y'shua's resurrection, it's clear that at the time the gospels were written, this was STILL their understanding of what the word "Sabbath" meant, else it would have caused widespread confusion for the writers of the gospels to have used the word "Sabbath" the way they did if they understood the word "Sabbath" to refer to Sunday.

Biblically, the Shabbat commandment was to rest on the 7th day of the week.  To do that, you have to know what the 1st day is, the 2nd, the 3rd, etc....thus some degree of tradition is required to interpret what the Scriptures means since there's no guide in the Bible on how to figure out what the 7th day is if you don't know it.

Jewish tradition has always associated the first day of the week as beginning Saturday night and ending Sunday night.  The second day begins Sunday night and ends Monday night...onto the 7th day, which is the Sabbath or Shabbat, which begins Friday night and ends Saturday night, starting the cycle all over again. Even those who promote observing Sunday as "the day" are forced to admit that the Bible does not recognize "moving" the Sabbath and that the Sabbath was traditionally considered Saturday.  This is because the logic they use for "moving" the Sabbath is that Y'shua (Jesus) rose on the first day of the week, according to Scriptures, which is Sunday.

Now let's check out what the Scriptures have to say on this though. Genesis / Bereshit 1:5 says...

"And there was evening, and there was morning--the first day."

So the Bible tells us a "day" runs from sundown to sundown, not "midnight" to "midnight" - a time keeping approach that came from Rome.  Now if someone tells you that the proper time for the Sabbath is midnight Sunday to midnight Monday, you know they have to be wrong because that does not line up with the Biblical definition of a day.

The book of Acts covers about a 30 year period, and not once in that 30 year period is there any mention of "moving" the Sabbath.  In fact, we see many accounts in Acts where they clearly continued to observe the Sabbath.  See Acts 13:14, 15:21, 16:13, 17:2, 18:4.

Gen/Ber 2:3 says,

"And God blessed the seventh day and made it holy, because on it he rested from all the work of creating that he had done. "

Now note that it says "God blessed THE SEVENTH DAY" not "God blessed the act of resting once every 7 days".  So there's a blessing on the 7th day that does not exist on the first day of the week.  So why not rest on the day that carries with it a blessing? Seems like if you don't rest on that day, you miss out on the blessing that comes with that day.  And since "God's gifts and callings are irrevocable" (Romans 11:29), it would be inconsistant for a God who "changes not" (Malachi 3:6) to change this.  There's just no Biblical evidence that the Sabbath was ever moved to the first day of the week.

In the Hebrew Language, the word for "seventh" and "Sabbath" both come from the same root word.  So the very definition of the words are intricately tied together.

Not only is there no Biblical evidence that the Sabbath was ever moved, but there's some Biblical evidence it was not.  For example, we have in Acts 20:7 et seq it reads...

"On the first day of the week we came together to break bread."

This is probably referring to the Jewish tradition of "Havdallah".  After the Sabbath is over, Jews often gather together for a Havdallah meal on Saturday night and discuss what they learned during their study time on the Sabbath.  Note that it goes on to say...

"Paul spoke to the people and, because he intended to leave the next day, kept on talking until midnight."

Now "The next day" would, of course, be Sunday.  Thus, Paul was travelling on a Sunday, not in a worship service, yet the Mosaic Law forbade travelling on the Sabbath.  Another verse that indicates that the Sabbath wasn't moved to Sunday is 1 Cor 16:2, which says...

"On the first day of every week, each one of you should set aside a sum of money..."

Jewish tradition interpretted the Sabbath commandment of rest to mean you could not spend money on the Sabbath and even banned carrying money on Shabbat (Mishnah Shabbat 24:1).  If you were out somewhere on Friday afternoon and it became dark, you were suppose to hand your money over to a gentile you could trust.  You could not even bring money to the synogogue to give it to the congregation.  They don't pass collection plates in the synogogues - you brought your money on OTHER days of the week and dropped it off in a box they had by the doors.  In order to donate money in Jewish tradition, you have to go out of your way to do it and then do something you're never asked to do in service, because they don't believe in passing collection plates.  You might find one that does it on a Tuesday night or some other day of the week, but on Shabbat, no Orthodox synagogue (shul) would ever pass a collection plate.    So if Paul is telling believers to deal with money on the first day of the week, then obviously the first day of the week was not some "new" Sabbath day.

We also find that the Mishnah teaches that one was to pay their tithe before the Sabbath arrived, not on the Sabbath. It tells us...

3 words a man must state in his house on the eve of Shabbat at dusk "Have you tithed?..." (Shabbat 2:7)

Here we see that one was suppose to have already paid his tithe by this time. Another place where this principal appears in Bekhorot 9:5, which says...

E. And why did they say the 29th of Elul (6th month) and they did not say the first of Tishre (7th month)?
F. Because it is a festival, and it is not possible to tithe on the festival.

Now tithing on a festival day is HUMANLY possible, but would be considered a violation of the commandment to treat this day as a Sabbath day as it says in Lev 23:23...

"On the first day of the seventh month you are to have a sacred Sabbath/(day of rest)..."

...thus dealing in money, including the giving of money to the synagogue, was therefore banned.

 

Are We Ever Told Sabbath is "For Today/Future"?

We're told that Sabbaths/Shabbats will be celebrated in the Millenium in Isaiah/Yeshayahu 66:23. And in Matthew 24:20 Y'shua said "Pray that your flight will not take place in winter or on the Sabbath".  Why?  The "winter" argument is obvious and travel in banned on Shabbat.  I forget where in the Bible it says not to "leave camp", but it is in there somewhere.  But getting back to the point, Y'shua was still talking about a "Sabbath" existing in the "end times" or "tribulation" period between His resurrection and the Millenium.

So who changed the Sabbath?

The Catholic Church claims they did. In The Convert's Catechism of Catholic Doctrine, p. 50, it states...

Q. Which is the Sabbath day?
A. Saturday is the Sabbath day.
Q. Why do we observe Sunday instead of Saturday?
A. We observe Sunday instead of Saturday because the Catholic Church transferred the solemnity from Saturday to Sunday."

The Council of Florence cursed anyone celebrating the original Sabbath, saying...

"The Most Holy Roman Church believes, professes, and teaches that the Mosaic law cannot be observed without the loss of eternal salvation.  Everyone, therefore, who observes circumcision and the Sabbath and the other requirements of the law, the Church declares not in the least fit to participate in eternal salvation."

Interpretative Levels

God gave the commandment to observe the Sabbath in plain language in the 10 commandments. There's no need to read between the lines or casually observe the fact that God wanted this done because Israel was doing it. We're told in plain simply language that God wants us to keep the 7th day as holy. Would God change that through just a hint? Some people have tried to say that 1 Cor 16:2 is "proof" that God changed the Sabbath. But even if you accept that interpretation, you still have to admit that it only hints at the idea that the Sabbath was moved to a different day - it doesn't come out and say that in plain language. Would a God who does not change (Mal 3:6) not only change His clear plain teaching, but do it with nothing more than a mere hint?

Summary

So in summary, we have seen that...

• Believers in the book of Acts keep the Biblical Sabbath
• History records that believers in most parts of the world kept the Biblical Sabbath until the 4th century AD.
• Sunday observance in Christianity began in Rome and Alexandria circa 100 AD, and spread to other areas around the 4th century AD.
• The Bible talks about the Sabbath in the future tense.

So why not keep the day that the earliest believers of the gospel kept?