The following is taken from Lily Ross Taylor's _The Divinity of the Roman Emperor_, Philological Monographs, no. 1 (Middletown, Conn: American Philological Association, 1931).
This post deals with PROSKUNHSIS
"The Greek word PROSKUNHSIS denotes an act of devotion to a god that consisted either in kissing the hand toward the image or--less often--in kissing the ground before it. The Greeks used the word to describe the Persian custom of greeting the king by bowing down and kissing the earth. Alexander's conquest of the great Persian empire had brought him into close contact with Persian customs and manners, and in general he found it wise to adopt them" (pp. 18-19).
"Of course the PROSKUNHSIS did not always imply 'worship' in our sense of the word. It was a form of greeting extended among the Persians by inferiors to those far above them (Hdt. 1.134). For an analysis of the material on the PROSKUNHSIS, see Schnabel, Klio, XIX, 118ff."
The full reference for the article to which Taylor refers is
Paul Schnabel, "Die Begründung des hellenistischen Königskultes durch Alexander," Klio 19 (1925) 113-27.