  We present supersymmetric soliton solutions of the four-dimensional heterotic
string corresponding to monopoles, strings and domain walls. These solutions
admit the $D=10$ interpretation of a fivebrane wrapped around $5$, $4$ or $3$
of the $6$ toroidally compactified dimensions and are arguably exact to all
orders in $\alpha'$. The solitonic string solution exhibits an $SL(2,Z)$ {\it
strong/weak coupling} duality which however corresponds to an $SL(2,Z)$ {\it
target space} duality of the fundamental string.
