summer half and a winter half, as attested in Old English and medieval Scandinavian sources. In Scandinavia this continued after Christianization; in Norway and Sweden the first day of summer is marked by the (14 April) and the first day of winter by the Calixtus Day (14 October). The month names do not coincide, so it is not possible to postulate names of a Common Germanic stage, except possibly the names of a spring month and a winter month, and . The names of the seasons are Common Germanic, , , , and for "spring" in north Germanic, but in west Germanic the term was used. The Common Germanic terms for "day", "month" and "year" were , and . The latter two continue Proto-Indo-European , , while is a Germanic innovation from a root meaning "to be hot, to burn". A number of terms for measuring time can be reconstructed for the proto-Germanic period. Month names Medieval Bede's Latin work De temporum ratione (The Reckoning of Time), written in 725, describes Old English month names. Bede mentions intercalation, the intercalary month being inserted around midsummer. Charlemagne (r. 768–814) recorded agricultural Old High German names for the Julian months. These remained in use, with regional variants and innovations, until the end of the Middle Ages in German-speaking Europe and they persisted in popular or dialectal use into the 19th century. They probably also influenced Fabre d'Eglantine when he named the months of the French Republican Calendar. The only agreement between the Old English and the Old High German (Carolingian) month names is the naming of April as "Easter month". Both traditions have a "holy month", the name of September in the Old English system and of December in the Old High German one. A separate tradition of month names developed in 10th-century Iceland, see below. Modern The Old High German month names introduced by Charlemagne persisted in regional usage and survive in German dialectal usage. The Latin month names were in predominant use throughout the medieval period, although the Summarium Heinrici, an 11th-century pedagogical compendium, in chapter II.15 (De temporibus et mensibus et annis) advocates the use of the German month names rather than the more widespread Latin ones. In the late medieval to early modern period, dialectal or regional month names were adopted for use in almanacs, and a number of variants or innovations developed, comparable to the tradition of