A Christmas tree is a decorated tree, usually an evergreen conifer such as spruce, pine, or fir or an artificial tree of similar appearance, associated with the celebration of Christmas. Originally a Celtic custom, the Christmas tree developed in early modern Germany (where it is today called Weihnachtsbaum or Christbaum) with predecessors that can be traced to the 16th and possibly 15th century, in which devout Christians brought decorated trees into their homes. It acquired popularity beyond Germany during the second half of the 19th century, at first among the upper classes.