Caltrops were typically placed on roadways to slow attacking troops traveling by vehicle or animal.

The caltrop was “the simplest weapon we ever made” according to Dr. Stanley Lovell, author of Of Spies and Stratagems. No matter how the caltrop is tossed, it will land with one of its four prongs up. Whatever rolls over it will be punctured or injured. It is effective when many are scattered onto enemy roadways or airport runways.

Historically, caltrops have been found in Babylonian tombs, were used against medieval knights on horseback, and were found in archaeological digs at Jamestown.

For a bunch of cool spy stuff that might not be relevant here and the source: https://www.cia.gov/legacy/museum/artifact/caltrop-tire-spike/