  We characterise the positive cone of a real C*-algebra geometrically. Given
an open cone $\Omega$ in a real Banach space $V$, with closure $\overline
\Omega$, we show that $\Omega$ is the interior of the positive cone of a unital
real C*-algebra if and only if it is a Finsler symmetric cone with an
orientable extension, which is equivalent to the condition that $V$ is, in an
equivalent norm, the hermitian part of a unital real C*-algebra with positive
cone $\overline\Omega$.
