John Lightfoot on Mark 15:21

[Coming out of the country, or field.] "They bring wood out of the field [on a feast-day], either bound together, or from some place fenced round or scattered." The Gloss there is; "They bring wood on a feast day out of the field, which is within the limits of the sabbath, if it be bound together on the eve of the feast-day, &c. A place watched and fenced in every way." And Rambam writes, "Rabbi Jose saith, If there be a door in such a fenced place, although it be distant from the city almost two thousand cubits, which are the limits of the sabbath, one may bring wood thence."

It may be conceived, that Simon the Cyrenean came out of the field thus loaded with wood; and you may conceive that he had given occasion to the soldiers or executioners, why they would lay the cross upon him, namely, because they saw that he was a strong bearer; and instead of one burden, they laid this other upon him to bear.