The primitive object may also be relinquished, and new ones proposed, with new lines and new plans of operations.

As he advances far from his primitive base, he forms new depots and lines of magazines.

He may encounter natural and artificial obstacles.

To cross large rivers in the face of an enemy is a hazardous operation; and he requires all the art of the engineer in constructing bridges, and securing a safe passage for his army.

If a fortified place is to be taken, he will detach a siege corps, and either continue his march with the main army, or take a strategic position to cover this siege.