  We give a natural construction of unramified over Z framed mixed Tate
motives, whose periods are the multiple zeta values. Namely, for each
convergent multiple zeta-value we define two boundary divisors A and B in the
moduli space M_{0,n+3} of stable curves of genus zero. The corresponding
multiple zeta-motive is the n-th cohomology of the pair (M_{0,n+3} -A,B).
