Mark had formerly accompanied Paul, and then Peter. Under Peter's guidance Mark also wrote the Gospel, which for this reason was called by some Peter's Gospel.
Several cities were known by the name Babylon. They bore this name in memory of the ancient and famous city of Babylon, the capital of the kings of Babylon. It had been destroyed by Cyrus and, in the time of the apostles, was a desolate heap of ruins with a very insignificant population.
One Roman military station in Egypt, near the present city of Cairo, was called Babylon. More populous was the city of Babylon built by Seleucus Nicator at the confluence of the Euphrates and the Tigris. According to Josephus, this city was more often called Seleucia.
Many Jews lived there. From them, of course, a small Christian Church was first formed there. But it is more correct to understand Babylon in an allegorical sense as the city of Rome.
Rome is so named because of its likeness to corrupt, idolatrous, power-loving, and proud Babylon. The great capital of the universal pagan empire, the city of Rome, was often called Babylon in Jewish writings and in the Apocalypse; see Rev 14:8; Rev 16:19; Rev 17:5, 8; Rev 18:2.
Many ancient interpreters understood Rome under the name Babylon, for example Clement of Alexandria, blessed Jerome, Oecumenius, Theophylact, and others.
The presence of the apostle Mark in Babylon also indicates that Rome should be understood by this Babylon. He was staying there around this time, as is clear from the epistles of the apostle Paul; see Col 4:10; Phlm 1:24. Tradition also confirms this.
The greeting of the Roman Church could be especially consoling and edifying for the Christians of Asia Minor. That Church flourished despite its dwelling at the center of all the abominations of the pagan world, and despite every hostility and oppression from the pagan world.
All the more could it console them because in this greeting one can see the expression of unity of mind with them and a bond of love.