Giambattista Nolli oriented his celebrated 1748 map of Rome with north up, a modern, carefully chosen cartographic convention, one that we still use today. It has the Tiber running more or less vertically towards the left side of the plate, the bulk of the city in the center, and the Vatican on the top-left corner.
Nolli owed greatly to a 1551 map by Leonardo Bufalini. But Bufalini had oriented his map with east up, following an earlier convention dating to the Middle Ages (see note.) In this map, the Tiber runs horizontally on the bottom half of the image, with the Vatican on the bottom-left corner. Among the 19 plats of his "Pianta Grande di Roma", Nolli actually included a reproduction of Bufalini’s plan, redrawn and reoriented with north up.
In 1774 Giovanni Battista Piranesi published his “Pianta di Roma e del Campo Marzo” with north down. Why? Piranesi had worked with Nolli in the 1748 publication--the “Piccola Pianta” is signed “Piranesi e Nolli incisero”--so he is quite deliberate in choosing a different orientation. One possible explanation is that he was going back to an experiential reading of the map, following the pilgrimage route from the north, entering the city through Porta del Popolo at the bottom of the drawing and proceeding up.
Note: for a more general discussion of the orientation of maps see an earlier blog entry.
(With thanks to old and new friends, Nick De Pace, Ezio Genovesi and Allan Ceen, for their guidance as I begin to to learn about Rome and its maps.)