It is not known for certain when the horizontal line or lines, which indicate an abbreviation, first came to be drawn through the L. The pound became an English unit of weight and in England became defined as the tower pound (equivalent to 350 grams) of sterling silver. The symbol derives from the upper case Latin letter L, representing libra pondo, the basic unit of weight in the Roman Empire, which in turn is derived from the Latin word, libra, meaning scales or a balance.
