The eighteenth century was much given to ingenious contrivances, and longitude had been constantly on its mind: what more natural than an efflorescence of meridian lines thruout Europe?

Since churches were a town's most prominent, central, and accessible public buildings, sundials are found on their outer walls, and sometimes, when there was money in the community and a large dark church, we also find the specialized sun indicators known as meridian lines. If you are going to put a pinhole in a southern wall and register the sun's passage on a line on the floor, you need a rather large space to make the meridian accurate, a dark one to make it readable, and money to do the job carefully; the principle is very simple, but the execution has to be quite precise to allow generations of townspeople to come in and set their watches by the device.

In the 18c, Fossombrone was rich from its silk weaving industry, and its cathedral was large and dark; a local mathematician named Sempronio Pace did the job in 1780.

In this photograph, you can just make out the pinhole, in the upper part of the vault of the S apsidal chapel.