It must have been quite an effort to construct the forum of Carsulae. Carsulae is a strange place: it was situated along the Via Flaminia, precisely at the point where it crosses the watershed between two tributaries of the Tiber – the Nera on the south and the Naja on the north. Coming from Rome and Narni, the Via Flaminia ascends into the city, reaching its highest point just before the Arco di San Damiano, which was the north entrance to the city. From there, it begins a descent through the necropolis towards the north. The ascent was pretty steep. Worse, the Via Flaminia ran through a depression, and was surrounded by slopes rather than by the flat plain needed to construct a forum square. In other words: to build the forum, it was necessary to construct a terrace.
The forum was constructed in the Augustan period, on the west side of the Via Flaminia, with a basilica on the east side. The level chosen for the terrace was such that the street and the forum met on the far north side of the forum, so that the two monumental temples on the south of the forum towered over the Via Flaminia. In this area (shown on the picture here), the height difference between the forum and the street was about five meters, and staircases were constructed to allow an easy passage for pedestrians. Yet the situation also created commercial opportunities. These were promptly acted upon by the designers of the forum: in the terrace that supported the temples, three tabernae were carved out. Obviously, this was about the best possible commercial location in town: directly on one of the major roads through the Italian peninsula, in the heart of the city.
We do not know for what kinds of businesses these tabernae were used in the three centuries of their existence, but it is highly likely that they were publicly owned, and brought in money for the local authorities in the form of vectigalia. The use rights of the shops could be traded between indivdual people. It is likely that the use rights in this location were extremely expensive, which limited the range of businesses that could be made profitable here. Evidence from other cities suggests that this could make it difficult for those involved in food retail and most forms of manufacturing, but we do not know enough of the urban landscape of Carsulae to be sure that this also was the case here.
It does not matter much. What matters is that here, like in so many cities, those involved in designing public buildings were keen to construct tabernae if they saw an opportunity, even directly (and visibly) underneath monumental temples on the forum. Apparently, and contrary to what some classical scholars have suggested in the past, Roman authorities saw little spatial tension between grand urban monuments and everyday urban commerce.