The great military frontiers of a state, especially when strengthened by natural and artificial obstacles, such as chains of mountains, rivers, lines of fortresses, &c., are regarded as permanent lines of defence.
The Alpine range between France and Piedmont, with its fortified passes; the Rhine, the Oder, and the Elbe, with their strongly-fortified places; the Pyrenees, with Bayonne at one extremity and Perpignon at the other; the triple range of fortresses on the Belgian frontier--are all permanent lines of defence.

The St.Lawrence river is a permanent line of defence for Canada; and the line of lake Champlain, the upper St.
Lawrence, and the lakes, for the United States.
Temporary lines of defence are such as are taken up merely for the campaign.

Napoleon's position in Saxony, in 1813; the line of the allies in Belgium, in 1815; the line of the Marne, in 1814, are examples of temporary lines of defence.
It will be seen from these remarks that lines of defence are not necessarily bases of operation.
_Strategic positions_ are such as are taken up during the operations of a war, either by a _corps d'armee_ or grand detachment, for the purpose of checking or observing an opposing force; they are named thus to distinguish them from tactical positions or fields of battle.

The positions of Napoleon at Rivoli, Verona, and Legnano, in 1796 and 1797, to watch the Adige; his positions on the Passarge, in 1807, and in Saxony and Silesia in front of his line of defence, in 1813; and Massena's positions on the Albis, along the Limmat and the Aar, in 1799, are examples under this head.
Before proceeding further it may be well to illustrate the strategic relations of lines and positions by the use of diagrams.
(Fig.

1.) The army at A covers the whole of the ground in rear of the line DC perpendicular to the line AB, the position of the enemy being at B.
(Fig.