This article analyses the phenomenon of glass in wall and floor opera sectilia from the Hellenistic period to Late Antiquity. This type of decoration was developed in Alexandria – as testified by archaeological finds – and then spread across the Greco-Roman world. In Rome the art created a backdrop for a series of displays – especially in imperial palaces and elite housing – that spanned the Imperial era. All the great metropolises were graced by it, including the new capital of the East, Constantinople, where it underwent a renewed flowering. This article analyzes the use of glass material mostly as inserts in marble compositions and, more rarely, in wholly vitreous compositions. It reflects upon the meaning of these different decorative products and attempts to interpret their economic, aesthetic, and symbolic implications.