A sword of ice-brook temper. Of the very best quality. The Spaniards used to plunge their swords and other weapons, while hot from the forge, into the brook Salo [Xalon], near Bilbilis, in Celtiberia, to harden them. The water of this brook is very cold.
“It is a sword of Spain, the ice-brook temper.”
Sævo Bilbilin optimam metallo Et ferro Plateam suo sonantem Quam fluctu tenui sed inquieto Armorum Salo temperator ambit.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894