Easton's 1897 Bible Dictionary:

Thyatira
   a city of Asia Minor, on the borders of Lydia and Mysia. Its
   modern name is Ak-hissar, i.e., "white castle." Here was one of
   the seven churches (Rev. 1:11; 2:18-28). Lydia, the seller of
   purple, or rather of cloth dyed with this colour, was from this
   city (Acts 16:14). It was and still is famous for its dyeing.
   Among the ruins, inscriptions have been found relating to the
   guild of dyers in that city in ancient times.


Hitchcock's Bible Names Dictionary (late 1800's):

Thyatira, a perfume; sacrifice of labor