(Luke 2:2; RSV, "enrolment"), "when Cyrenius was governor of Syria," is simply a census of the people, or an enrolment of them with a view to their taxation. The decree for the enrolment was the occasion of Joseph and Mary's going up to Bethlehem. It has been argued by some that Cyrenius (q.v.) was governor of Cilicia and Syria both at the time of our Lord's birth and some years afterwards. This decree for the taxing referred to the whole Roman world, and not to Judea alone. (See CENSUS .)
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Taxing'". "Easton's Bible Dictionary".