Indeed, they could not well be built before hostilities commenced, as their locality in each case must be determined by the position of the hostile forces.
Having already described the general influence of permanent fortifications as a means of national defence, we shall here speak merely of the principles of their construction.

It is not proposed to enter into any technical discussion of matters that especially belong to the instruction of the engineer, but merely to give the nomenclature and use of the more important parts of a military work; in a word, such general information as should belong to officers of every grade and corps of an army.
The first species of fortification among the ancients was of course very simple, consisting merely of an earthen mound, or palisades.

A wall was afterwards used, and a ditch was then added to the wall.

It was found that a straight wall could be easily breached by the enemy's battering-rams; to remedy this evil, towers were built at short intervals from each other, forming a broken line of salient and re-entering parts.

These towers or salient points gradually assumed a shape approximating to the modern bastion.
After the invention of gunpowder and the application of cannon to the attack and defence of places, it became necessary to arrange earthen ramparts behind the thin walls of the ancient works, for the reception of the new artillery.