“ A special technical use of the term is in fortification, where it is applied to a work or series of works constructed in rear of existing defences in order to bar the further progress of the enemy should he succeed in breaching or storming these. A modern example may be found in the siege of Port Arthur in 1904. When early in the siege Fort Panlung fell into the hands of the Japanese, the Russians connected up the two adjacent first-line forts to a fort in the rear by means of new works, the whole forming a rough semicircle facing the lost fort. ”