  Even though Peltesohn proved that a cyclic (v,3,1)-design exists if and only
if $v\equiv 1,3\pmod{6}$ as early as 1939, the problem of determining the
spectrum of cyclic (v,k,1)-designs with k>3 is far from being settled, even for
k=4. This paper shows that a cyclic (v,4,1)-design exists if and only if
$v\equiv 1,4\pmod{12}$ and $v\not\in\{16,25,28\}$.
