RORY: What is the oil for?
LORELAI: For pouring on Visigoths.
The Visigoths, an early Germanic people. Under their first leader, Alaric I, they invaded Italy and sacked Rome in 410. They later settled in southern Gaul and Hispania (modern France and Spain), and maintained a presence there from the 5th to the 8th century AD.
Lorelai refers to the popular idea of medieval castle defenders pouring boiling oil onto their assailants in order to protect themselves during a siege. There are only a few known instances of it actually happening (none against the Visigoths).
Historians think that the oil would have been hot, rather than boiling, and that it had the added advantage of making everything too slippery to climb. It probably wasn’t used very often, as oil was so expensive that hardly anyone had enough of it in stock. Boiling water and hot sand were far more commonly used.
The Annotated Gilmore Girls 