The library is planned as an open, clear and luminous construction that floats over the Roman remains. It incorporates both the archaeological vestiges and the geometry of the traces of modern Ljubljana. The four blocks of program are placed around a central void drawn over the Cardus and Decumanus crossing, the resulting perimeter adapts to the current urban grid. The patio organizes the different parts of the Library, while a light skin wraps the ensemble. The gaps between the enveloping façade and the built areas define a series of void vertical spaces that look towards the city. The final volumes have different heights, regarding the nearby constructions, and a common folded roof plan unifies them all. Thanks to a perimeter structure that permits the creation of large open areas, interiors are designed as flexible and versatile spaces. This structure rests on a sort of “cantilever tray” that protects the archaeological remains underneath.