A book of hours was a personal manuscript belonging to a wealthy patron, containing prayers to be read at set hours of the day. From 1412 three Netherlandish brothers — Paul, Jean and Herman de Limbourg — worked on such a book for Jean, Duke of Berry, brother of the King of France. In 1416 all three brothers and their patron died, most likely of plague; the book was left unfinished and completed by other hands seventy years later.

The twelve calendar pages that open the book mark a break in medieval painting. Each month is shown through the labour of its season: peasants warming themselves in the February snow, the harvest, the grape gathering, the herding of pigs. Faces and clothing are drawn from observation, and snow appears for the first time in European painting as a convincing white cover. In the backgrounds stand the duke's actual castles — Saumur, Lusignan, the Louvre — at recognisable accuracy. The sky is laid in lapis lazuli and the light in gold leaf; the cost of the materials is a reminder of whom the page was made for.

The spatial depth is not yet mathematical — Brunelleschi's perspective experiment would come a few years later, around 1415 in Florence. The Limbourgs build depth by observation, by scale and by colour. This is why the book is a bridge between two periods: its subject is still the religious calendar while its gaze is worldly. The calendar pages were reproduced so widely in the twentieth century that much of our common visual image of medieval life comes directly from this manuscript.