Barcelona before the Romans
Just what happened to the Iberian cultures in those centuries when Spain was nominally becoming a Roman province? We might look for an example at Barcelona which has been extensively explored.

Showing sites of the Iberian period in the hills behind Barcelona. The main settlement was on Montjuic, while the Roman town was laid out on the flat ground beside it
Barcelona today is set in the middle of the fertile plain surrounded by low mountains, but at the centre of the semicircle, there is one anomaly, a steep hill known as Mont Juic. Roman Barcelona was built sensibly to one side as it is too steep for sensible habitation and Medieval and modern Barcelona has followed suit, though the town spreads over much of the wonderfully fertile plain. The fine National Museum of Catalonia is built to one side with a marvellous view of the plain, and when Barcelona hosted the 1992 Olympic Games, Montjuic was made a centre of attraction.
To pre-modern eyes however, Montjuic was very attractive. It forms a fine defensive position and it was near the mouth of the Llobregat river, which was navigable up into the hills. And here a town arose between the fourth and second centuries BC.

One of the main features of these Iberian settlements were these huge circular pits which were presumably silos for storing grain
The most distinguishing feature of the settlements were the great silos, huge pits up to 6 m wide, and a similar depth. Some good examples were found in excavations in advance of a new railway in 1946.

View of one of the silos excavated in 1946. The person at the bottom of the silo gives an idea of its scale and capacity.
They appear to have been granaries for storing grain in huge amounts – enough to last 245 people for a whole year. It appears to have been a society based round grain – the cultivation of the vine did not come until later. There are a number of structures that could be houses and a drystone wall a metre wide that could be a defensive wall. It could have been a major village in Iberian times, not unlike Emporion, the Greek trading port 140 km further north.
No habitation of this period is known in the surrounding plain, but in the hills behind, a dozen or more sites have been discovered, many of them marked by deep silos. However all these sites appear to date to between the 5th and 2nd centuries BC — there is a gap in the first century BC till the founding of Barcelona as a Roman colony around 10 BC. What happened to all these settlements in this gap? Had there been a war with the Romans, and the Romans wiped them all out? No trace of any destruction has been found. Or had they decided to move to a safer territory further inland? But in 10 BC a Roman town was founded. The reorganisation by Augustus was extremely successful and the new town, Barcino, flourished. Indeed it has continued to flourish down to the present day.
Header: view inland across the plain of Barcelona from the terrace of the National Art Museum of Catalonia on Montjuic.