As Jesus was carrying his cross to the place of execution, a man named Simon of Cyrene was compelled by soldiers ( Matthew 27:32; Mark 15:21; Luke 23:26 ) to carry Jesus cross. Possibly referring to the legal right of a soldier to require a provincial to carry his gear one mile for him. Mark calls him "the father of Alexander and Rufus" without further explanation, probably taking it for granted that his readers would all know who Rufus and Alexander are. The Christian writer Papias (died around 130 AD) tells us that Mark originally wrote his Gospel for the Christian community in Rome. This suggests that Alexander and Rufus were well known to, and probably part of, the Christian congregation in Rome. Very possibly their father Simon had himself become a Christian, though this must remain conjecture. 

And they compel one Simon a Cyrenian, who passed by, coming out of the country, the father of Alexander and Rufus, to bear his cross (Mark 15:21)