From the Wikipedia entry on "Middle Ages"
Until the Renaissance (and for some time after that), the standard scheme of history was to divide history into six ages, inspired by the biblical six days of creation, or four monarchies based on Daniel 2:40. The early Renaissance historians, in their glorification of all things classical, declared two periods in history, that of Ancient times and that of the period referred to as the "Dark Age". Filippo Villani first mentioned a "middle period" between Antiquity and his present when he observed in a treatise of 1382 that the islands in the Mediterranean Sea were called by different names in priscis mediis modernisque temporibus ("primitive, middle, and modern times"). In the early 15th century, it was believed history had evolved from the Dark Age to a new period with its revival of things classical, so some scholars, such as Flavio Biondo, began to write about a middle period between the Ancient and Modern, which became known as the Middle Age. It was not until the late 17th century when German scholar Christoph Cellarius' published Universal History Divided into an Ancient, Medieval, and New Period that the tripartite periodization scheme began to be used more systemically.
2 ^ John Burrow. A History of Histories. 2007. ISBN 978-0-7139-9337-0 - see page 416 for Christoph (Keller) Cellarius.