After they left the walled city of Jerusalem, Jesus became too weak to carry his cross. The Roman soldiers forced Simon of Cyrene (a city in northern Africa) to carry it (see Matthew 5:41).
Usually, a person being crucified had to carry the horizontal crossbeam (called the patibulum) to the place of execution. The vertical post (called the stipes) was often left in the ground as a warning to others (like a hangman’s scaffold in a public square).
Simon of Cyrene, the father of Alexander and Rufus: These men were probably known to Mark's audience (see Romans 16:13).
Golgotha is an Aramaic word, meaning The Place of the Skull. In the Latin Vulgate, "skull" is calvariae ("Calvary"). In the time of Jesus, Golgotha was outside the walls of Jerusalem (John 19:20; see Matthew 27:32; Hebrews 13:12). When Herod Antipas later enlarged the city with the so-called third wall, Golgotha was enclosed.