Abatis

An abatis, abattis, or abbattis is a field fortification consisting of an obstacle formed (in the modern era) of the branches of trees laid in a row, with the sharpened tops directed outwards, towards the enemy.

Gregory of Tours mentions the use of abatises several times in his writing about the history of the early Franks.

He wrote that the Franks ambushed and destroyed a Roman army near Neuss during the reign of Magnus Maximus with the use of an abatis.

He also wrote that Mummolus, a general working for Burgundy, successfully used an abatis to defeat a Lombard army near Embrun.

A form of giant abatis, using whole trees instead of branches, can be used as an improvised anti-tank obstacle.

Abatisses are used in war to keep the approaching enemy under fire for as long as possible.
Abatis improvised by Japanese troops during World War II
Giant abatis, made from entire trees, can make an effective anti-vehicle obstacle. This formation can be achieved by use of explosives—note the splintered stumps
Abatis can be defeated by dozer blades , as fitted here to a British Challenger 2 tank