What makes March so special?... in zodiac terms?
Pure speculation on my part, but it is spring-- daylight is returning.. and in a agracultureal community, it is the start of the year. even in pre-agraculturual communities, the spring markes the beginning of life. herding animals often have biological cycles that time birth to the spring.

Ireland's old celtic new year is February 1st-- the beginning of lambing.. the 4 major seaonal holidys are Feb 1, Begining of summer, May 1 Summer, August 1, Midsummer, Nov 1, death of summer. (death of summer was also the death of the year, and marked the time that all who had died during the year crossed over into the spirit land.. so on the eve of the death of the year, the spirits of the dead arose, and started there journey to the other world.. this is still celebrated as halloween.)