What is "chevaux de frise"

Usage examples of "chevaux de frise".

He squinted up into the sun dazzle at the narrow parapet around the open observatory dome, where the barrels of the Xlasers protruded in a glittering chevaux de frise.

The country was mostly forest, difficult for troops to work in, especially for the Macedonian phalanx, for unless they can make a kind of chevaux de frise with the extraordinarily long spears which they hold in front of their shields - and this requires a free and open space - they are of no use whatever.