In ancient Egypt, the Goddess Bast was a black, female cat. Christians, wanting to rid society of all traces of other religions, convinced the ignorant that black cats were demons in disguise and should thus be destroyed. The kindly ladies who cared for the cats were often destroyed in the process, being condemned as witches.
A demon black cat crossing your path would create a barrier of evil, cutting you off from God and blocking the entrance to heaven.
Read more: http://www.dazeinfo.com/2010/06/22/superstitions-across-different-countries-an-overview/#ixzz3DsRZTOmI