ClipArt ETC
"A Castle is a building constructed for the purpose of repelling attack. The castella left by the Romans were constructed on the general model of their stationary encampments, and though they may have suggested the castles of the Middle Ages, they differed from them in being designed for military purposes only, and not as places of permanent residence."—(Charles Leonard-Stuart, 1911)

Castle

"A Castle is a building constructed for the purpose of repelling attack. The castella left by the Romans…

"Tower of a German Feudal Castle." -Foster, 1921

Feudal Castle Tower

"Tower of a German Feudal Castle." -Foster, 1921