I was born in Mexico, and my last name is Maciel. From what I can tell, it's probably of French or Portuguese origin. Maciel sounds a lot like many other last names that are corruptions of the French word Monsieur and, at least to me, sound like it could come from Mon ciel--->Monciel--->Maciel. It's probably originally of French origin but from what I can tell no longer exists there. Also, the first record I have ever found of the name Maciel was in the late 1700's (I think) in Portugal. Either way, it could have been imported to the Americas by various routes, to Brazil via Portugal and to Mexico via France (during the French intervention in Mexico). The name seems to be pretty common in some rural areas of the cnetral Pacific states of Mexico, in villages where people are generally a bit isolated historically and largely of European descent. Hope this helps.