Abstract: A polygonal carton constructed from a unitary blank of stiff but foldable material and having a strong, weight supporting bottom. The carton has a plurality of side panels and a concave bottom. The bottom is formed from a plurality of triangularly shaped bottom panels equal in number to the side panels. Each bottom panel is hingedly connected to one of the side panels and inclines upwardly from the bottom edge of the side panel to the center of the carton bottom. A foldable web is hingedly connected to and between the abuting side edges of adjacent bottom panels. Each web is folded into a reinforcing rib above or below the carton bottom. The ribs hold the panels in place as and when a load is placed on the bottom and the load is supported, at least in part, by the locking and bearing engagement between abuting side edges of adjacent bottom panels.