Greeks and Romans reclined to dine

Elagabalus's guests being smothered when the petals were released from a large net above the table

Art historians have often noted that banqueters almost always appear to be reclining on their left sides. The usual explanation is that lying on the left leaves the right hand free to hold the dining vessels. When lying on the left, the chewed food has room to expand because the curvature of the stomach is enhanced in that position. The lesser curvature on the right side of the stomach gives little space for food to resist the increased abdominal pressure and so lying on the right will soon cause reflux. For the ancient Mediterranean civilizations, the evening meal lasted hours, and involved a lot of eating and drinking. Lying on the left would not just have reduced the risk of reflux, it would also have provided space for the large amounts of food the revellers were required to eat.

https://www.nature.com/articles/448753a