The purpose of this paper is to classify all compact manifolds modeled on the 4-dimensional solvable Lie group Sol1 4 , and more gener- ally, the crystallographic groups of Sol1 4 . The maximal compact subgroup of Isom(Sol1 4 ) is D4 = Z4 ⋊ Z2. We shall exhibit an infra-solvmanifold of Sol1 4 whose holonomy is D4. This implies that all possible holonomy groups do occur; the trivial group, Z2 (5 families), Z4, Z2×Z2 (5 families), and Z4 ⋊ Z2 (2 families).