2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/65709We study surfaces constructed from groups of units in quaternion orders $Λ$ over the integers in real quadratic fields k. A short presentation of some general theory of such surfaces is given, in particular, we construct certain ``modular curves'' on the surfaces and examine their properties. We apply our results to some surfaces related to the case $k=Q(\sqrt{13})$ and $d(Λ)=(3)$, and find their place in the Kodaira classification of algebraic surfaces.15 pagesAlgebraic GeometryNumber Theory14G35; 11G18text