Proskynesis

Proskynesis (/ˈprɒskɪniːsɪs/; Greek προσκύνησις) proskynesis (from the words πρός pros (towards) and κυνέω kyneo (to kiss)) is described by the Greek researcher Herodotus of Halicarnassus, who lived in the 5th century BC in his Histories 1.134:

When they meet each other in the streets, you may know if the persons meeting are of equal rank by the following token: if they are, instead of speaking, they kiss each other on the lips. In the case where one is a little inferior to the other, the kiss is given on the cheek; where the difference of rank is great, the inferior prostrates himself upon the ground.