Donald Lateiner, a humanities-classics professor at Ohio Wesleyan University, says that men kissed men on the cheek as a social greeting, while subjects of a king "abased" themselves by kissing the ground in front of him.
While speaking at a press conference in Chicago, he said that people who wanted to curry favour with someone of higher status would "kiss up" the person's hands, shoulders, and head-in that order.
He revealed that peems, novels, and all kinds of art helped him parse out the history of the kiss.
Lateiner said that many Tuscan and Roman ladies' mirror cases sported erotic scenes "from the world of myth, (or) sometimes from the world of daily life."
However, on Athenian vases and Pompeian frescoes, romantic smooching is quite rare.
"(Instead) there's a whole lot of sex," National Geographic quoted him as saying.
He said that that might be because artists of the era preferred to depict full bodies, and a "Hollywood close-up" of people kissing would be too small a detail to feature.
Anthropologist Helen Fisher of Rutgers University highlighted the fact that over 90 percent of human societies and several animals, including chimpanzees, used kisses to express themselves.
She said that the ubiquity of the smooch supported Charles Darwin's belief that kissing was an instinct that evolved to jump-start reproduction.
The two researchers presented their findings on kissing during the annual meeting of the American Association for the Advancement of Science.