The text says they went out without saying what they were going out of, but “out of the city” seems most likely.

Came upon is best understood to mean “happened to find” or “happened to meet.”

Cyrene was a Greek city on the north coast of Africa. For some it is helpful to say “the city of Cyrene.” Simon is also mentioned by Mark (15.21) and Luke (23.26). He may have been someone well known in the Christian community to which Mark wrote, because there he is further identified as “the father of Alexander and Rufus.” For Matthew he seems to have been no more than a name.

That the soldiers forced Simon to carry Jesus’ cross is not exceptional. The rigors of the trial and of the beating which followed would have left Jesus physically exhausted. It was customary for the condemned man to carry the cross beam (not the entire cross) on his shoulder; the upright of the cross would have remained in a stationary position at the site of execution. Cross was discussed previously at 10.38. Here translators can say “board (or, beam) on which they would execute him (or, put him to death).”

Compelled translates the same verb used in 5.41; see comment there. They forced Simon to carry his cross. Some have to specify “Jesus’ cross.”

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .