A triclinium (plural: triclinia) is a formal dining room in a Roman building. The word is adopted from the Greek τρικλίνιον, triklinion, from τρι-, tri-, "three", and κλίνη, klinē, a sort of "couch" or rather chaise longue. Each couch was wide enough to accommodate three diners who reclined on their left side on cushions while some household slaves served multiple courses rushed out of the culina, or kitchen, and others entertained guests with music, song, or dance.
The triclinium was characterized by three klinai on three sides of a low square table, whose surfaces sloped away from the table at about 10 degrees. Diners would recline on these surfaces in a semi-recumbent position. The fourth side of the table was left free, presumably to allow service to the table. Usually the open side faced the entrance of the room. In Roman-era dwellings, particularly wealthy ones, triclinia were common and the hosts and guest would recline on pillows while feasting.
The Museum of Archeology in Arezzo, Italy, or the House of Caro in Pompeii offer what are thought to be accurate reconstructions of triclinia. The custom of using klinai while taking a meal rather than sitting became popular among the Greeks in the early seventh century BC. From here it spread to their colonies in southern Italy (Magna Graecia) and was eventually adopted by the Etruscans.
In contrast to the Greek tradition of allowing only male guests into the formal dining room, called andrōn, while everyday meals were taken with the rest of the family in the oikos, the Etruscans seem to not have restricted the use of the klinē to the male gender. The Romans may have seen the first dining klinai as used by the Etruscans but may have refined the practice when they later came to closer contact with the Greek culture.