In the corner of Santa Llúcia and Bisbe Streets, we find a corious thing that does not call the atention of any of the tourists who walk around the cathedral of Barcelona. On the romanic chapel of Santa Llúcia, erected three decades before the construction of the Cathedral, we find this semicircular column sculpted in stone on the wall which measures exactly one “destre cane”.
The word “cane” is engraved on the wall next to the column so everybody in the Medieval barcelona could check that this was the standard measure of longitude in the market.
A cane (from the latin qana) was an ancient unit of mesurement used on the Crown of Aragon, part of France and the north of Italy. Before the Internacional Sistem of Units it was a way to have a fixed reference of lenght. This unit was used for building specific sticks of wood that were used on the market tents to have a reference when they were selling. In Barcelona, it was equivalent to eight palms, six feet or two steps, that is about 1.55 meters, although it wasn’t exactly the same measure everywhere. For example, in Tortosa it was equivalent to 1.59 meters but the reference to the whole Catalan countries was the same as in Montpellier, equivalent to 1.99 meters. Furthermore there were the square cane which was used to measure surfaces: in Barcelona it was equivalent to 2.44 square meters, 2.42m. in Girona , 2.43m in Tarragona and in 2,45m in Mallorca. Surprisingly we see that there is less diference between the square canes than in the lenght measures. As we’ve said, it was the unit of longitude used in the markets next to the cathedral in the Middle Ages althought the Catalan “destre cane” was also used. It was equivalent to twelve palms and this is exactly the height of the column that we find next to the cathedral.
This post has been written by Ander Castillo and Robert Salla in the subject Història de les Matemàtiques (History of Mathematics, 2014-15)
Location: Carrer de la Pietat 2 (map)