"Sapping."

Our speech abounds in words which have survived only in a phrase, and which, if taken out of the phrase, sound unfamiliar. We all speak of illness as "sapping one's strength." That phrase comes from medieval warfare. The return of the present war to medieval siege tactics has brought "sapping" back to its original sense.

In the Middle Ages besieged cities were surrounded by a wall, and the wall was surrounded by a moat. The sapper (or miner) dug under ground until he reached the foundations of the wall. Here he built a shelter by leaning beams against the wall to protect him while he undermined its foundations. As fast as he made a breach in the wall he propped it with beams to keep it from tumbling on him as he worked. Finally he set fire to the beams and fled, leaving the wall to cave in as the supports burned away.

The defenders of the wall, meanwhile, amused themselves by dropping heavy stones on the beams of the lean-to shelter or by pouring down boiling oil.

Today the sappers burrow from the front trench under No Man's Land and blow up the enemy trench with high explosives.

A political surprise is described as "springing a mine." Indeed, it is hard to find any vocabulary of politics or of philosophy which does not not reek with figures of speech borrowed from the battlefield. --Boston Globe.