1st Peter could have been written before 41 AD.

So people insisting Babylon can't be Babylon in 1 Peter and Revelation like to talk about Josephus account in Antiquities Of The Jews Book 18 Chapter 9 of the Jewish community in Babylon being forced to leave for Seleucia in 41 AD as evidence Peter wouldn't have gone there with no Jewish population left.

One website mistakenly says 41 BC, I think that's just a typo though.  This event is the end of Book 18, it follows the entire reign of Tiberius and all or most of the reign of Caligula, so it happened in 40 AD at the soonest.

Now I've responded to this in a few ways in the past.  First Trajan's account clearly has Babylon still existing and populated in the teens of the second century.  Lots of sites online insist on talking about this account as if it says Babylon was nothing but a ruin, they are just over emphasizing Trajan's disappointment at it's decline, but it's also clear people were still living there as at least one Temple was till operating as Trajan offered sacrifices to Alexander in the room where he died.  Therodoret of Cyrus refers to Babylon still being inhabited in the fifth century.

And I've also argued that Peter could mean Babylon as in the region of Babylonia, not just the individual city of Hammurabi and Nebuchadnezzar.  The Babylonian Talmud is called the Babylonian Talmud for a reason.  I agree with those who say the Babel of Genesis 11 was probably Eridu.  And in Seleucia both the Gentile and Jewish population were of people who were moved there from Babylon, they may well have called themselves Babylon in some sense.  The Jewish Population of Seleucia got involved in the Kitos War during the reign of Trajan.   The Assyrian Orthodox Church had a Bishopric in Babylonia till well after the Muslin Conquest, often based in Seleucia.

 However I also feel it's highly possible 1 Peter was written before 40 AD.  I place the Crucifixion in 30 AD, and the events of Acts chapters 6 through most of 11 in 36/37 AD, maybe getting into early 38 at the latest.  By then Believers were being called Christians at Antioch and Peter was done with his affairs in Joppa and Caesarea.

The Death of Herod Agrippa recorded in Acts 12 was in 44 AD.  We tend to assume the Passover season when James was martyred and Peter imprisoned was the one of that same year, and if true it perfectly leaves room for Peter to have been in Babylon during that gap.  But it's also possible the narrative of Acts 12 after verse 19 jumps forward to record his death.  It might be the end of Acts 11 and beginning of Acts 12 is supposed to be at the very start of the reign of Claudius, Herod Agrippa didn't become King of Judea till Claidus came to power.  I think it's possible Peter and James were in Jerusalem for this Passover because it was Pilgrimage festival, their being here isn't evidence no one left Judea yet.

Don't get deluded by any notion it'd take a long time for Christian Communities to emerge in the places Peter wrote to.  Pentecost of Acts 2 included Jews from those same parts of Asia and Mesopotamia.  The communities Paul started later were the primarily Gentile ones, 1 Peter is specifically addressed to Jewish Believers of the Diaspora.

Paul said Peter was in charge of bringing The Gospel to the Circumcision in Galatians 2:7-8, and for over 600 years by this time Babylonia had the most important Jewish community outside of Israel.  Rome had a Jewish population (also represented at Pentecost) but it was much smaller and less significant.  So Peter would be remiss in his duties if he didn't go to Babylonia.

The idea that Peter would use Babylon as code for Rome to hide what he's talking about from the Roman authorities is absurd.  Besides negative assumptions we make about the name Babylon, Peter isn't saying anything bad about this city, just that it's is where he is, and presumably so is Marcus.  And if any authorities had intercepted the letter they could easily have known where it as mailed from and so using a derogatory code name could only be counter productive to that presumed goal.

Now all that said, I have been contemplating the Babylon in Egypt theory, and may make a post on that soon, though frankly my thoughts there are more about that being The Babylon of Revelation.

The oldest traditions do not assume every Mark or Marcus of The New Testament was the same person.  And I unlike most don't even think every John Mark was the same, fact is among Romanized Jews of the first century John Mark was likely the equivalent of John Smith.  The John Mark associated with Paul and Barnabas is probably the cousin of Barnabus mentioned in the Epistles.  The John Mark son of Mary of Acts 12 I think is the one Peter mentions in his Epistle and who wrote the Gospel According to Mark.

I believe The Gospel According to Mark was based on what Peter preached in Babylonia, and I agree with the arguments for it and Matthew both being written already before the events of Acts 12.

Biblical Prophets were not cowards, when Babylon was the current world power Old Testament Prophets didn't use Nineveh as code, no in the Old Testament Nineveh is Nineveh and Babylon is Babylon.  So I'm tired of people saying that Revelation's "Old Testament imagery" proves Babylon is Rome.

If you respect Tradition so much, the Assyrian Orthodox Church traditionally holds that Peter was exactly where he says he was when he wrote that Epistle.