Factory lamps (or Firmalampen) are utilitarian in nature and quite simple in appearance. Characteristically they have a channeled nozzle, plain discus, and 2 or 3 depressions on the base with matching protrusions or bumps on the shoulder. These convex and concave elements function like modern day Lego, allowing the lamps to be securely stacked one on top of another.
Factory lamps were initially manufactured in Northern Italy and Southern Gaul between the late first and third centuries AD. They were widely distributed across the Mediterranean and commonly imitated in the European Provinces. The vast majority have been stamped to indicate production centres.