The new NUKII National and University Library is located in the historic center of Ljubljana a few meters from the University Library Joze Plecnik on a site occupied by the Roman ruins of the ancient city of Emona. The vast program of 20.000m2 is compacted in a single volume that adapts the small plot and looks for a formal autonomy as a public building. The architectural composition shows the weight, seriousness and environment of the old library building by Plečnik by setting up a clear central area surrounded by “thick walls”. A central open space which hosts the open acces library and public facilities stands in contrast to a closed peripheral space that accommodates the closed storage, support program and administration. The “thick wall” that embraces and protects the interior is presented as a Vierendeel beam like a great skeleton that makes it possible to leave the Roman ruins almost untouched by the structure. The interior platforms are suspended from this skeleton without reaching the perimeter allowing the whole interior to bathe in natural light. The image of the solid construction is conferred by a structural grid as a support of the black stainless steel plates which give dense and hermetic character to the building.