A first voussoir for use in an arched structure between second and third voussoirs includes a first end bearing surface with a protrusion which extends from the surface and which is mateable with a corresponding recess in an abutting end bearing surface of the second voussoir. The second end bearing surface includes a recess in the surface which is mateable with a corresponding protrusion in an abutting end bearing surface of the third voussoir. Preferably the protrusions and the recesses have both longitudinal and transverse components of structure. A connector is secured to the first voussoir for connecting one end of an associated tension member to the first voussoir while an opposed end of the tension member is connected to an associated mooring positioned at a distance away from the horizontal span of the arched structure. Arched structures comprising a plurality of such voussoirs may be constructed by successively positioning individual ones of the voussoirs in arching abutment to form a segment of the structure, then positioning a keystone. During construction, individual voussoirs may be moored to associated moorings to avoid the need for underlying shape support. After construction, they may remain moored to impart added stability to the structure.