  In this short note we study flat metric connections with antisymmetric
torsion $T \neq 0$. The result has been originally discovered by
Cartan/Schouten in 1926 and we provide a new proof not depending on the
classification of symmetric spaces. Any space of that type splits and the
irreducible factors are compact simple Lie group or a special connection on
$S^7$. The latter case is interesting from the viewpoint of $G_2$-structures
and we discuss its type in the sense of the Fernandez-Gray classification.
Moreover, we investigate flat metric connections of vectorial type.
