Created on thick stock paper using Alberti’s Horizon instrument. 380mm diameter.
Alberti’s Horizon is an instrument that allows any person to recreate the map of Rome using a radial co-ordinate system invented by Alberti. The city walls, gates, river and significant buildings were all measured and mapped from a central point in the city, each being given a radial distance (on a horizontal plane) and degrees from N at the central point. These are laid out in tables so that they can be transcribed using the instrument.
The horizon instrument is made up of a ring of a user defined diameter divided into 48 degrees and 4minutes per degree. A rule divided into 50 sections with each section containing 4 minutes sits so that it pivots from the centre allowing for radial measurements.
Users therefore read off the co-ordinates from the tables and find them using the rule. For example a co-ordinate of 28’3″, 43’2″ would be found by rotating the rule to an angle of 28 degrees and 3 minutes, then reading off the rule the point of 43’2″ and mark this on the page. This is continued through all the tables and in the case of the walls of the city require you to join the dots to form the map.