  In a previous paper we define a Curtis-Tits group as a certain generalization
of a Kac-Moody group. We distinguish between orientable and non-orientable
Curtis-Tits groups and identify all orientable Curtis-Tits groups as
  Kac-Moody groups associated to twin-buildings.
  In the present paper we construct all orientable and non-orientable
Curtis-Tits groups with diagram $\widetilde{A}_n$ over a field ${\mathbb F}$.
The resulting groups are quite interesting in their own right. The orientable
ones are related to Drinfel'd' s construction of vector bundles over a
non-commutative projective line and to the classical groups over cyclic
algebras. The non-orientable ones are related to q-CCR algebras in physics and
have symplectic, orthogonal and unitary groups as quotients.
