For a brief narrative of the siege of Port Arthur in 1904, one of the greatest sieges of history, both as regards its epic interest and its military importance, the reader is referred to the article RUSSO-JAPANESE WAR.
DEFINITIONS.--The following definitions may be useful, but have no place in the evolution of the attack, to which this section is mainly devoted.
_Investment._--This most necessary, almost indispensable operation of every siege consists in surrounding the fortress about to be besieged, so as to cut off its communications with the outside world. _Preliminary investment_ which is carried out by cavalry and light troops before the arrival of the besieging force, consists in closing the roads so as to shut out supplies and reinforcements. _Close investment_ should be of such a character as to prevent any sort of communication, even by single messengers or spies. The term "_blockade_" is sometimes loosely used instead of investment.
_Lines of Circumvallation and Contravallation._--These now obsolete terms were in great use until the 19th century. The _circumvallation_ was a line of parapet which the besieger made outside the investing position of his own force, to protect it when there was a chance of attack by a relieving army. The line of _contravallation_ was the line of parapet and trench sometimes made by the besieger all round the town he was attacking, to check the sorties of the garrison.
_Observing Force._--When circumstances make the reduction of a particular fortress in the theatre of operations unnecessary a force is often detached to "observe" it. The duty of this force will be to watch the garrison and prevent any hostile action such as raids on the lines of communications.
_Bombardment._--This operation, common to all ages, consists in a general (sometimes an indiscriminate) fire against either the whole target offered by the fortress or a particular section of that target. In ancient and medieval times the effect of a bombardment--whether of ordinary missiles, of incendiary projectiles, or of poisonous matters tending to breed pestilence--upon a population closely crowded within its walls was very powerful. In the present day little military importance is attached to bombardment, since under modern conditions it cannot do much real harm.