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.  Moreover these walls were soon found inadequate to resist the missiles of the besiegers, and it became necessary to replace them by parapets of earth.  In order to cover the retaining walls of these parapets from the besieging batteries, it was also found to be necessary to lower these walls as much as possible, and to raise the counterscarps.  The traces or plans of the works, however, received no material change till about the close of the fifteenth century.

It is not known who first changed the ancient towers into bastions.  Some attribute it to an Italian, and with considerable show of reason, for a bastion was built at Turin as early as 1461.  Achmet Pacha, it is said, fortified Otranto in this way, in 1480, but whether the system was previously known among the Turks cannot be determined.  Others attribute the invention to Ziska, the celebrated leader of the Hussites.  It is most probable that the transition from the tower to the bastion was a very gradual one, and that the change was perfected in several countries at about the same time.

Fortifications, like other arts and sciences, greatly flourished in Italy under the Medicis, and that country furnished Europe with its most skilful engineers.  Catharine of Medicis introduced into France many of her countrymen, distinguished in this profession; among these may be named Bellamat, Bephano, Costritio, Relogio, Vorganno, the two Marini, Campi, and Hieronimo, who built several important places and directed the sieges of others.  These able foreigners were rivalled by some distinguished French engineers, who laid the foundation of the “corps du Genie” which has since become a school of military instruction for the world.  Among the early French engineers may be distinguished Lafontaine De Serre, Feuquieres, and St. Remy.  Pedro Navarro had been appointed a member of this corps, but his attention was more specially directed to mining, and we do not learn that he distinguished himself in the construction of any fortification.

In Germany, in the beginning of the sixteenth century, Albert Durer distinguished himself as a writer on fortification; his book is remarkable as containing the germs of many of the improvements which were made by those who followed him.  This is the more to be wondered at as he was not a professed engineer.  After him followed Spekel, a native of Strasburg, who died in 1589.  His writings are valuable as showing the state of the art at that time, and the changes which he himself introduced.  He was an engineer of much practical knowledge and experience, having assisted at the sieges of Malta, Golletta, Vienna, Jula, Nicosia, Famagusta, &c.