Considerable latitude is allowed in selecting sites for batteries. For convenience of supply and unity of command they should be collected in groups, the batteries of the groups separated by at least 100 to 200 yards; and the groups should be located, so far as other considerations allow, near the main lines of communication. If these groups do not entirely surround the place, they should, when practicable, extend at least half way around, so as to bring a reverse fire on all covers. The fire, once opened, should continue night and day. If a conflagration breaks out, a sharp fire of shells should be directed upon it and its vicinity to prevent its extinction. Special efforts should be made to blow up magazines and destroy shops, storehouses, docks, roads, bridges, or other communications useful to the defence; but, so far as is practicable consistently with these, an attempt should be made to avoid injury to public monuments, museums, antiquities, and works of art. Bombardments are sometimes commenced and continued for a longer or shorter time without the expectation of reducing the place, but to destroy some of the constructions above mentioned or to prevent the completion or arming of a work which it is intended to attack by other methods. A slow bombardment may also precede the active cannonade which prepares for an assault, or the systematic artillery attack of a regular siege. DEFENCE AGAINST BOMBARDMENT. =8.= The defence against bombardment is frequently, from necessity, strictly passive, and consists in so disposing the troops and materials as to protect them under bomb- and splinter-proofs, repairing damages to the latter and to magazines and parapets as occasion offers; saving the ammunition of the place by firing only such shots as promise to pay for themselves by the effect produced; and reserving all the strength of the place to meet the subsequent attack, if made. When circumstances admit, a more active defence may be made, by a strong garrison, by well-conducted sorties which may capture and destroy the hostile guns and batteries and defeat and drive off their supports. Sorties of this kind may sometimes be profitably made against the flanks of the attacking force, or against isolated batteries, even when a general attack cannot be made. Opportunities for their use should not be neglected. CHAPTER II. SIEGE OR ATTACK BY REGULAR APPROACHES. PRELIMINARY CONSIDERATIONS, DEFINITIONS, ETC. =9.= By a regular siege is meant a systematic and more or less deliberate attack upon a fortified place, in which the besieger aims to invest the place and capture its fortifications in succession by regular approaches, beginning with the most advanced and ending only with the reduction of the innermost keep and the surrender of the garrison. The successive steps of a siege are usually the following: The investment. The artillery attack. The construction of parallels and approaches. Breaching by artillery or mines.