  In this paper, we give a natural construction of mixed Tate motives whose
periods are a class of iterated integrals which include the multiple
polylogarithm functions. Given such an iterated integral, we construct two
divisors $A$ and $B$ in the moduli spaces $\mathcal{\bar{M}}_{0,n}$ of
$n$-pointed stable curves of genus 0, and prove that the cohomology of the pair
$(\mathcal{\bar{M}}_{0,n}-A,B-B\cap A)$ is a framed mixed Tate motive whose
period is that integral. It generalizes the results of A. Goncharov and Yu.
Manin for multiple zeta values. Then we apply our construction to the
dilogarithm and calculate the period matrix which turns out to be same with the
canonical one of Deligne.
