is this little gem:

It's called a caltrop, or in Latin, tribulus, and is an anti-cavalry weapon. A nice article on the device can be found here.

This one is bronze, about 4.5cm (1 3/4 inches) high, has a nice green patina and the points are still very sharp. It is just sooo cool and nasty looking. A person or animal stepping on one of these at a run would be in a world of hurt.