The art by which a place is so fortified that a given number of men occupying it may advantageously oppose a superior force. The same word also signifies the works that cover and defend a place. Fortification is defensive when surrounding a place so as to render it capable of defence against besiegers; and offensive when comprehending the various works for conducting a siege. It is natural when it opposes rocks, woods, marshes, ravines, &c., to impede the progress of an enemy; and artificial, when raised by human ingenuity to aid the advantages of the ground. The latter is again subdivided into permanent and field fortification: the one being constructed at leisure and of permanent materials, the other raised only for temporary purposes.