The task of crossing a great river in front of an active foe is one of the most dangerous of all military operations.

Any serious miscalculation of the strength, the position, or the mobility of the enemy's forces may lead to an irreparable disaster; and until the bridges used for the crossing are defended by _tetes de pont_ the position of the column that has passed over is precarious.
[Footnote 135: Farcy, _La Guerre sur le Danube_, p.73.For other malpractices see Colonel F.A.

Wellesley's _With the Russians in Peace and War_, chs.xi.

xii.] [Footnote 136: _Punch_ hit off the situation by thus parodying the well-known line of Horace: "Russicus expectat dum defluat amnis."] The Danube is especially hard to cross, because its northern bank is for the most part marshy, and is dominated by the southern bank.

The German strategist, von Moltke, who knew Turkey well, and had written the best history of the Russo-Turkish War of 1828, maintained that the passage of the Danube must cost the invaders upwards of 50,000 men.