a thousand chariots

seven thousand horsemen

These are soldiers who rode on horses. "7,000 horsemen" (See: rc://en/ta/man/translate/translate-numbers)

These are soldiers who walked. "20,000 footmen" (See: rc://en/ta/man/translate/translate-numbers)

David had his soldiers cut the hamstring muscles on the backs of the horses' thighs so they would no longer be able to run.

to keep for a special use