Every habitation, whether it was a hut, hall, shed, lean-to or bothy, was dark and smoky inside.
To avoid the trouble of relighting it and for light and cooking, wood or peat fires were kept burning continually. A cauldron could be suspended from the roof beams above the central hearth.
No smoke hole or chimney overhead meant that the fish and meat hung among the roof beams were preserved by the chemicals in the smoke, giving the food a rich, tangy taste. Some smoke would eventually dissipate and seep through the thatch.
Early clay oil lamps were imported from Gaul, usually with no handle and the wicks made from pith of rushes.
Among the “barbarian” tribes of the colder climates of the North, beyond the reach of the legions, candles were made of tallow and animal fat due the scarcity of olive oil.
The tallow was rendered down in the cauldron over the hearth and then poured into shaped bronze moulds.
With the decline of the Roman Empire and the consequent disruptions to trade, luxuries like olive oil became scarce and tallow candles became increasingly widespread.
Red Branch Chronicles 