In my reading about medieval battles I haven't read about the use of CALTROPS , a sort three or four spiked jack with sharp points used in the medieval warfare to injure horses or deny the ground for their use. One would think that their use would have been to protect infantry from heavy cavalry charges similarly to the way antitank mines are laid in front of infantry positions to impede tanks and render them better targets for antitank weapons.

In combined arms operations which the English were famous for using, if an infantry formation adopted close order with spears such as schiltron then it could be attacked by the archers. If the infantry spread out to make a less desirable target or attacked the archers then they became the object for a heavy cavalry attack. There is the CRUX, how to keep an infantry formation safe from a heavy cavalry charge yet deny a suitable target for the archers? Its seems that caltrops would have been an ideal solution.

Has anyone done any reading on this weapon and where it was employed in a battle with success?

The Chinese used them. So did the Romans (called tribulus) and Persians. I thought the Japanese called them tetsubishi. Generally there were two sizes;.smaller ones for humans and larger ones for mounts (horses, camels, elephants, etc). One early recorded use of the caltrop was at Gaugamela (331bc) when the Persians tried to use them against the Macedonian cavalry. The largest deployment of caltrops was by the Chin against the Mongols at P'ei K'ou fort (1213). Apparently the ground was covered with caltrops up to a distance of 30 miles from the fort.