St. John the Evangelist holding the cup of poison that has already killed several others; in the background, John on the island of Patmos.

A book of hours is a type of devotional text that was popular in the Middle Ages, particularly in the late medieval period. It is a type of prayer book that contains a collection of prayers and devotional texts that were meant to be read at specific times of the day, known as the "hours." These texts were usually written in Latin and were intended for personal use by laypeople, although some were also used by monks and other religious figures. The book of hours typically included a calendar of feast days, psalms, and other prayers, as well as illustrations and decorations.

John was banished to Patmos by the Roman authorities during the reign of the emperor Domitian, where he wrote the book of Revelation, the final book of the New Testament. In works of art, St. John is often shown holding a book or scroll, symbolizing the text of Revelation, or with a quill pen, signifying his role as an author.