WE CLASSICISTS SPEND a lot of our time taking things on trust, without quite knowing how they can be true. The use of olive oil provides a good example. Every book on the 'Amazing Ancients' reports that olive oil was a multi-purpose product, used for lighting, cooking and cleaning and for making perfumes, cosmetics and medicines. Until now it has always been the last use that has had me baffled, but Patrick Faas explains all, and embarrassingly obvious it is too.

As today, olive oil came in different qualities in ancient Rome. First, there were the late-harvested olives that were turning black. These produced viridum ('green'), in three pressing, the last pressing being the low-grade oil used for cooling and lighting. (One litre of oil produces about 134 hours of light