Donato Labate (the archaeologist in charge of the dig) said (inter alia):
"We found a large ancient Roman dumping filled with pottery scraps. There were vases, bottles, bricks, but most of all, hundreds of oil lamps, each bearing their maker's name."
"It was indeed a commercial success. Fortis gained such a name for its lamps that its stamp was copied and reproduced throughout the empire. It was one of the earliest examples of pirated brands."
"We know now for sure that Fortis came from Mutina. The city was a major pottery center, a cluster of pottery workshops, as the variety of brand names on the newly discovered items testifies."
Just to give you an idea of how far afield a Fortis lamp might go, back in 2001 one was found at Carmarthenshire (Wales); photo and report at the BBC.
Ancient Roman Oil Lamp 'Factory Town' Found (Rossella Lorenzi, Discovery News)
Ancient Roman oil lamp 'factory town' found in Italy (New Kerala)
Ancient Roman oil lamp brand 'from Modena' (Italy Magazine)