The Riera Rambla
The most important torrentes, such as the riera Blanca and the d'Horta, covered the area between Montjuïc and the Llobregat with their deposits, one, and the Sant Martí wetlands, the other. Between both, a set of torrenteras and small streams filled the flatter ground between the small hills at the edge of the coast. Precisely one of them, the Mons Tàber, was chosen to locate Roman Barcino in the 1st century. But another of these hills, the hill of los Ollers, now completely disappeared, is the one that suggests the impossibility that the current Rambla was a natural riera at the time of the construction of the Roman wall and probably not before the 10th or 11th centuries, not underestimating streams that in times of heavy flooding could cover the entire area.
During the Barcino era, when the first wall was built at the lower part of the Rambla, approximately between where the streets Escudellers and Nou de Sant Francesc are today, the hill of los Ollers rose, forcing the coastline to form a bay, called de los Còdals, to the hill of las Falzies, where the Collserola riera used to flow back then. On the other side of the hill of los Ollers, there was a lagoon, called el Cagalell, where the waters from the Malla, Bargalló, and Magoria streams drained.
The Collserola riera received water from the southern slope of the mountain range that gave it its name, as well as from the hills of Putxet and Monterols. It seems that initially the riera, known at its source as Sant Gervasi, received water from the Vallcarca riera, but at an undetermined date, already with the city in place, this riera was diverted towards the course of the Torrent de l'Olla. There is no record of whether it was nature itself or humans who had something to do with it. In any case, during flooding times, the quantity and force of water from both rivers together would have been very impressive, enough to suggest to the citizens of Barcino - Barcelona the convenience of diverting the course of one of them.
The Sant Gervasi riera flowed down to the Travessera, where it was known as Riera de Sant Miquel, continued along the Passeig de Gràcia, and, now as the Collserola riera, entered the area of the current Ciutat Vella between the Portal de l'Àngel and Rivadeneyra street, and led to pl. de la Cucurulla, Pi street, pl. Sant Josep Oriol, and through Còdols street it emptied into the bay of els Còdals (a còdol is a small, smooth, rounded fragment of hard rock often found due to water erosion and rolling).
The Creu d'en Malla riera originated on the Monterols hill and also received water from the Modolell hill. It entered the city area at pl. de la Universitat, passed behind pl. de la Gardunya, and flowed into the Cagalell. Some authors believe that the d'en Malla riera is an artificial and relatively modern water conduit. In any case, it should not have been very significant.
The courses of these rivers were on both sides of the Rambla, separated by <>.
Pau Vila explained that the Rambla had never been a riera and that the confusion came from the equivocal interpretation of the toponym. Other authors debate this assumption, but anyway, when urbanization began, expanding through Ciutat Vella towards Raval, the rushing waters would have been very destructive and required diverting the course of the riera to where the Rambla is today.
This solution lasted no more than two centuries. The city's expansion and the construction of the third wall once again required diverting the riera, and now, the riera de Sant Gervasi, that of Sant Miquel, Collserola, and La Rambla became part of the Creu d'en Malla, allowing the Rambla to become the quintessential promenade of Barcelona.
