BIBLIOGRAPHY.--The more important works on the subject are: Durer, _Unterricht zur Befestigung_ (Nuremberg, 1527); Speckle, _Architectur von Festungen_ (Strassburg, 1589); Fritach, _L'Architecture mil. ou la f. nouvelle_ (Paris, 1637); Pagan, _Les Fortif._ (Paris, 1689); de Ville, _Les Fortif._ (Lyons, 1629); de Fer, _Introduction a la fortification_ (Paris, 1723); B.F. de Belidor, _Science des Ingenieurs, &c._ (Paris, 1729); works of Coehoorn, Vauban, Montalembert, Cormontaingne; Mandar, _De l'architecture des forteresses_ (Paris, 1801); Chasseloup-Laubat, _Essais sur quelques parties de l'artil. et de la fortification_ (Milan, 1811); Carnot, _Defense des places fortes_ (Paris, 1812); Jones, _Journals of Sieges in Spain_ (3rd ed., London, 1846); T. Choumara, _Memoire sur la fortification_ (1847); A. von Zastrow, _Geschichte der bestandigen Befestigung_ (N.D., Fr. trans.); works of Sir C. Pasley; Noizet, _Principes de fortif._ (Paris, 1859); Dufour, _De la fortif. permanente_ (Paris, 1850); E. Viollet le Duc, _L'Architecture militaire au moyen age_ (Paris, 1854); Cosseron de Villenoisy, _Essai historique sur la fortification_ (Paris, 1869); works of Brialmont (_q.v._); Delambre, _La Fortification dans ses rapports avec la tactique et la strategie_ (Paris, 1887); v. Sauer, _Angriff und Verteidigung fester Platze_ (Berlin, 1885); Schroeter, _Die Festung in der heutigen Kriegfuhrung_ (Berlin, 1898-1906); Baron E. v. Leithner, _Die bestandige Befestigung und der Festungskrieg_ (Vienna, 1894-1899); W. Stavenhagen, _Grundriss der Befestigungslehre_ (Berlin, 1900-1909); Plessix and Legrand, _Manuel complet de fortification_ (Paris, 1900, new edition 1909); Ritter v. Brunner, _Die bestandige Befestigung_ (Vienna, 1909), _Die Feldbefestigung_ (Vienna, 1904); Rocchi, _Traccia per lo studio della fortificazione permanente_ (Turin, 1902); Sir G.S. Clarke, _Fortification_ (1907); V. Deguise, _La Fortification permanente contemporaine_ (Brussels, 1908); Royal Military Academy, _Text-book of Fortification_, pt. ii. (London, 1893); British official _Instruction in Military Engineering_, pts. i., ii. and iv. (London, 1900-1908). (L. J.) FORTLAGE, KARL (1806-1881), German philosopher, was born at Osnabruck. After teaching in Heidelberg and Berlin, he became professor of philosophy at Jena (1846), a post which he held till his death. Originally a follower of Hegel, he turned to Fichte and Beneke (q.v.), with whose insistence on psychology as the basis of all philosophy he fully agreed. The fundamental idea of his psychology is impulse, which combines representation (which presupposes consciousness) and feeling (i.e. pleasure). Reason is the highest thing in nature, i.e. is divine in its nature, God is the absolute Ego and the empirical egos are his instruments.