The earliest evidence of a potentially-formal choir robe is found in ancient Greece. The Greek Chorus seems to have been relatively common in that era, and can be seen depicted on a portion of pottery dating from around 425 BC. That Greek pottery displays members of a choir both singing and playing musical instruments. The members of that ancient choir are seen wearing lengthy loose gowns that reach up and across their left shoulders. Those pictured in the pottery displayed to the left obviously have a slightly more elaborate design than the earliest depiction.
The use of gowns likely developed from the ancient tunic. Indeed, clerical vestments such as an alb are directly related to the ancient tunic, with the word origin being a latin phrase meaning a tunic of white. Modern albs remain a plain, lightweight, ankle-length tunic with long sleeves, with a rope cincture about the waist. Ancient tunics were sleeveless, and were seen as a distinction from barbarians wore sleeved clothing (probably because those tribes lived in the colder regions). The tunic eventually did include a sleeve around the 3rd century, after military leaders returned from a campaign wearing them. This combination of tunic and choir evolved with time.