Square bottles came into use in the AD 60s and rapidly became the commonest glass vessel form in the empire. For the next two centuries their fragments dominate all glass assemblages. Hitherto this material has not been exploited to any great extent because there has been no close chronological framework.
Blue/Green Glass Bottles from Roman Britain presents a classification scheme for the moulded base patterns which allows their chronological development to be reconstructed. With this it is possible to explore how sizes and capacities changed with time. The British data are set within the context of the bottles from the rest of the western empire, and it can be seen that different provinces favoured different base patterns in a systematic fashion. Previously it has been assumed that base patterns reflect long distance trade of the bottles and their contents. Now it can be seen that the main driving force for the distribution of bottles with similar distinctive base patterns was most probably the movements of military units, and that most bottles were made locally.
An investigation of common capacities indicates that these were shared with glass bath flasks and it is proposed that, just as bath flasks were oil containers for hygiene purposes, square bottles became so common because they were the favoured vessel for household oil. The chronological trajectories of square bottles, bath flasks and the Spanish olive oil industry evidenced by Dressel 20 amphoras are identical, but previously unremarked upon.