Today, I came across two changes in the arches of Lapa over the centuries. One being the removal of some of the smaller arches in order to widen them.
Photos above from the early 1960s. Below, late 1950s.
In 1872, the pillar in the middle of Rua dos Arcos was removed to improve transit (also, in 1948, a second pillar was removed, on Rua Mem de Sá). At the end of the 1960s and start of the ’70s, the government began a project to bring back the original form of the arches, reinstalling the missing pillars to what one sees today.
The second change I discovered carries with it some conflicting dates. I came across what I’d consider reliable information that, in 1906, Pereira Passos had illegal occupations in between the arches removed. That’s right, between the smaller arches along the bottom, there used to be make-shift houses where poor residents lived. The conflicting dates part comes into play because, as I understand it, the photo above is from 1911. Also of interest in this photo, the kiosks (so popular these days in Lisbon).