Albert Barnes Commentary Luke 23:26

"And when they led him away, they laid hold upon one Simon of Cyrene, coming from the country, and laid on him the cross, to bear it after Jesus." — Luke 23:26 (ASV)

See Barnes on Matthew 27:32.

After Jesus. Probably to bear one end of the cross. Jesus was feeble and unable to bear it alone, and they compelled Simon to help him.