Window V21 of Milan Duomo is dedicated to the Stories from the Old Testament. Together with the other two imposing stained-glass apse windows (V19 and V20) it is found behind the High Altar and is part of one of the most evocative glimpses into Gothic architecture from Duomo's first construction phase. The 135 original panels, worked on since the beginning of the 15th century, were completely replaced in the 19th century by the workshop of Giovanni Battista Bertini and his sons. In the upper part, some original panels can be found, while the panels visible in the lower register depict episodes from the Book of Genesis, amongst these are recognisable "God Creates Light", "Original Sin", "Adam and Eve", and "Noah's Ark".