When I pay a visit to someone who tells me he lives on the first floor, I usually walk up the stairs. Sometimes there is no choice, since the building has no lift. But then, often, especially on the floors of the Eixample and Ciutat Vella, this first floor easily ends up turning into a third!
The stairs of the buildings in Barcelona are full of semi-floors, mezzanines and main floors (principals). Moreover, in the past the heights of these floors were greater, so it is not strange that you have to climb considerably to get to that "first floor".
Previously, the most wanted floor was the first one, in order both to avoid the discomfort of the street and to not having to climb too many stairs. Up from this floor you could progressively find the families with more limited purchasing power.
This way, it was most prestigious to live on a first or a second floor than on the fourth floor. Naming the first floors as "mezzanine" and "principal", the third floor suddenly happened to be the first, and so gradually. Thus, all social classes could be at the same time in the same building, the city's social hierarchy was translated to the distribution of families in the buildings.