  We present a six-dimensional T^2/Z_2 orbifold model which arises as an
intermediate step in the compactification of the heterotic string to the MSSM.
The orbifold contains two pairs of inequivalent fixed points, with unbroken
local gauge groups SU(5) and SU(2)xSU(4), respectively, the intersection of
which gives the standard model gauge group. All bulk and brane anomalies are
cancelled by the Green--Schwarz mechanism. At each SU(5) fixed point, there is
a localised \bar{5}+10 standard model generation, while the third generation
and the Higgs fields come in split bulk multiplets due to the breaking of SU(5)
at the other fixed point.
