For more than 500 years the summer solstice has been marked in Florence by the gnomon in the city's cathedral, which, at 90 metres (295 feet) from the ground, is the highest in the world. The gnomon takes the form of a hole cut into a bronze plate, which is located under the south window of the church's octagonal lantern.
The gnomon was installed in 1475 by Paolo dal Pozzo Toscanelli (1397-1482), a Florentine mathematician, astronomer and cosmographer. Toscanelli was a friend of Filippo Brunelleschi (1377-1446) and a correspondent of Christopher Columbus (c.1451-1506).
At midday, on June 21st, a beam of sunlight passes through the hole creating a disk of light, which perfectly aligns with a disk of marble embedded in the floor of the Chapel of the Cross (north transept). The marble disk forms part of a meridian line.
A new meridian line was created in 1755 by Leonardo Ximenes (1716-86), a Jesuit priest and the grand-ducal astronomer.