The foundation includes an assembly of wooden components which interconnect to form an enclosed rectangular configuration for supporting a mattress. At each corner of the assembly are two posts which are interconnected by dowels or by a tongue and groove. The dowels and the mouths of the openings in which they are accommodated are bevelled for facilitating the insertion of the dowels into the openings should they be misaligned. The tongues and grooves are also bevelled for the same reason. The wooden components are subject to compressive forces and to a heat treatment before being assembled into the foundation.