These are practically immutable, and they doom to failure the side that, at the critical points, persists in standing on the defensive.

A study of the events around Plevna shows clearly what a brave but ill-trained army can do and what it cannot do under modern conditions.
From the point of view of strategy--that is, the conduct of the great operations of a campaign--Osman's defence of Plevna yields lessons of equal interest.

It affords the most brilliant example in modern warfare of the power of a force strongly intrenched in a favourable position to "contain," that is, to hold or hold back, a greater force of the enemy.
Other examples are the Austrian defence of Mantua in 1796-97, which hindered the young Bonaparte's invasion of the Hapsburg States; Bazaine's defence of Metz in 1870; and Sir George White's defence of Ladysmith against the Boers.

We have no space in which to compare these cases, in which the conditions varied so greatly.

Suffice it to say that Mantua and Plevna were the most effective instances, largely because those strongholds lay near the most natural and easy line of advance for the invaders.