Complex sentence: Local legend puts the origin of the captive raven population at the time of King Charles II (reigned 1660--1685); however, historians believe that the "Tower's raven mythology is likely to be a Victorian flight of fantasy".
Split into simpler sentences: Local legend puts the origin of the captive raven population at the time of King Charles II (reigned 1660--85). Some historians believe the "tower's raven mythology is likely to be a Victorian flight of fantasy".