Complex sentence: For a period in the late 19th century Roger van der Weyden was attributed, Duchesne-Guillemin, 129 or at least an artist familiar with the outline of Liège, in today's Belgium.
Split into simpler sentences: For a period in the late 19th century Roger van der Weyden was attributed. See Duchesne-Guillemin, 129 and probably by an artist familiar with the outline of Liège, in today's Belgium.