Revettments.—­Every trench at points needs support, and this revetting may be done with any of the following materials:  Sod; corduroy of logs laid lengthwise; sand bags (size 20 in. x 10 in. x 5 in.); galvanized iron; chicken wire and cloth made in a frame about six feet long; hurdles, wicker mats made by driving three-inch stakes into the ground, leaving uprights as high above the ground as the depth of the trench, then weaving withes and slender saplings between the uprights; expanded metal; gabions, cylindrical baskets made like hurdles except that the stakes are driven in a circle; fascines, bundles of faggots about 10 inches in diameter by 9 feet long.  The faggots are laid together on a horse or between stakes driven in the ground, then “choked,” or bound tightly together, by a rope 3 feet 8 inches long with loops at each end, tightened with two stiff levers.  The bundle is then bound with wire at intervals of two feet.  The circumference of a fascine should be 25 inches.

[Illustration:  Plate #17]

Capt.  Powell of the C.E.F. found during 18 months’ service in the trenches, that a separate construction for the bottom and firing step from that of the parapet made repair much simpler when the trench was damaged by shell fire.  The upper part of the trench usually suffers most, while the bottom section, if unattached, often remains intact and the drainage system needs only to be cleared out.  If the portion above the firing step is one piece with that below, however, the whole trench has to be reconstructed.

There is nothing more important than the supports used to keep revetting in place.  With sods, sand bags, concrete and gabions, a proper arrangement in the first place will make other support unnecessary.

Sod should be placed carefully, with a slope of not more than one inch on four, with the vegetation uppermost.  This type is least affected by rain.

Sand Bags should be used like brickwork, laid in alternate headers (binders) and stretchers.  Their use should be confined as far as possible to emergency and repair work, because after a few weeks the bags rot and cannot be moved about.  If the trench wall has been demolished by artillery fire, the particles of cloth make digging out the bottom of the trench a very difficult matter.

Concrete Work has been used extensively by the Germans, but the chips fly like bullets under shell explosion, and the concrete cracks and disintegrates in severe weather.  It is used in the bottom of trenches for drainage and for the firing step.

Gabions may be set into the wall of the trench and filled with earth, or used at corners to prevent the wearing down of the edge, which reduces the protective effect of the trench.  Set in at a slight angle they will hold the side without further re-enforcement.