"This back (eastern) side is adorned with a small niche framed by an elaborate rendering of a double-headed deity, probably Itzamna. Within the niche is a small sculpted human figure seated cross-legged. This niched figure is recognized as an accession motif at the Maya site of Piedras Negras, located along the Usumacinta river far to the northwest of Quirigua. Based on this accession motif, it can be assumed that Monument 9 commemorates the inauguration of a Quirigua ruler, probably Jade Sky, around the year 800 A.D."
Robert J. Sharer, Quirigua: A Classic Maya Center & Its Sculptures, Carolina Academic Press, 1990, p. 48-9