§ 1. The practical duties of buildings are twofold.

They have either (1), to hold and protect something; or (2), to place or carry something.

1. (1.) Architecture of Protection. This is architecture intended to protect men or their possessions from violence of any kind, whether of men or of the elements. It will include all churches, houses, and treasuries; fortresses, fences, and ramparts; the architecture of the hut and sheepfold; of the palace and citadel; of the dyke, breakwater, and sea-wall. And the protection, when of living creatures, is to be understood as including commodiousness and comfort of habitation, wherever these are possible under the given circumstances.

2. (2.) Architecture of Position. This is architecture intended to carry men or things to some certain places, or to hold them there. This will include all bridges, aqueducts, and road architecture; lighthouses, which have to hold light in appointed places; chimneys, to carry smoke or direct currents of air; staircases; towers, which are to be watched from or cried from, as in mosque, or to hold bells, or to place men in positions of offence, as ancient moveable attacking towers, and most fortress towers.

§ 2. Protective architecture has to do one or all of three things: to wall a space, to roof it, and to give access to it, of persons, light, and air; and it is therefore to be considered under the three divisions of walls, roofs, and apertures.