Adam Clarke on Matthew 27:32

A man of Cyrene - him they compelled to bear his cross - In John, Joh 19:16, Joh 19:17, we are told Christ himself bore the cross, and this, it is likely, he did for a part of the way; but, being exhausted with the scourging and other cruel usage which he had received, he was found incapable of bearing it alone; therefore they obliged Simon, not, I think, to bear it entirely, but to assist Christ, by bearing a part of it. It was a constant practice among the Romans, to oblige criminal to bear their cross to the place of execution: insomuch that Plutarch makes use of it as an illustration of the misery of vice. "Every kind of wickedness produces its own particular torment, just as every malefactor, when he is brought forth to execution, carries his own cross." See Lardner's Credib. vol. i. p. 160.