The Codex Athous Dionysiou is a 10th-century illuminated manuscript of the Old Testament, known for its intricate decorations and is housed at the Dionysiou Monastery on Mount Athos. It is considered one of the finest examples of Byzantine art due to its elaborate and exquisite decorations. The manuscript is not only a religious text but also a remarkable piece of historical art, reflecting the rich cultural and artistic heritage of the Byzantine era.