Where does the expression "to gird your loins" come from, and what exactly does it mean?

To gird is often used to mean prepare, make ready, or draw up strength, but literally it means to bind, tie, or surround. To gird your loins can mean to get ready for a rumble or to put on your underwear. If it's the former then I think the idea is that covering one's balls lends some confidence in a fight.

gird = base word for girdle?

The expression is Biblical in derivation, a traveler would raise his tunic up and fasten it up with his belt to free his movement and keep it from dragging in the dust.

i agree with biblical times. thought it was to fasten up robe to run or fight, thus girding(encircling one's loins)

actually, it goes back a bit farther than the bible... in the epic of gilgamesh, the oldest known text, the title character refers to his recently deceased best friend and fellow adventurer as "you, my festal garment, a sash over my loins--"

“Gird up your loins like a man; for I will demand of you, and answer thou me” Job 38:3, 40:7

The book of Job predates most of the books of the Bible, according to the scholarly.

To gird your loins during the Roman Era meant to draw-up and tie your lower garment between your legs as to increase your mobility and agility