In his treatise entitled Horologi Elementari (Venice, 1669), Domenico Martinelli explains one of the features of the hour display in Italy, namely: the division by 6 and not by 12 of the dials of clocks and watches. He calls them "6 hour clocks in the manner of Rome". A process that dates back to mediaeval times. Its origin appears to lie in the monastic tradition of dividing the day and night according to prayer times, with the day starting at midday. Commonplace throughout Italy on clocks from the 15th to the 17th centuries, this form of display fell from use in the north of the peninsula in the early 18th century following the adoption of duodecimal time. It was still regularly used, however, in the central and southern parts of the peninsula up to the Napoleonic Wars.