Which of the following best describes the seating arrangement in a triclinium?

The seating arrangement in a triclinium is best described as couches positioned around a rectangular table. This setup reflects the dining practices of ancient Rome where a triclinium typically featured three couches (generally referred to as "lecti") placed on three sides of a low table, allowing diners to recline while eating and socializing. The arrangement was designed for comfort, reflecting the social importance of dining in Roman culture, where guests would recline on their left side, propped up by pillows, to enjoy their meals in a leisurely manner.

The other options do not accurately represent the triclinium's design. The circular formation of chairs does not align with the traditional three-sided arrangement, and sitting mats spread across the floor or stools against the walls suggest more casual or communal settings rather than the formal dining experience embodied by the triclinium. The correct answer embodies the essence of how individuals interacted during meals in ancient Roman social settings.