|Fortifications and castles|
Every fortification satisfies the needs of a wider and more complex defence system. Therefore, the design of military artefacts depended on the choice of location, construction typology and the role that a fortification was meant to play. In addition to the urban fortifications and those situated close to urban settlements, some towers survive that now appear isolated but probably were once part of a more complex and interconnected defence system (for example, the network of coastal towers or those located along the course of the river Biferno). Architectural traces survive on outcrops of rock in impervious, and therefore naturally defensible positions, which are still hard to reach and sometimes even to recognise because of their dilapidated state; or more rarely, on fluvial plains (as at Celenza sul Trigno). These are fortified elements that were once used for sighting or the control of traffic (located on elevated ground such as at Oratino on the Ponte della Zittola-Lucera or the Venafro-S.Croce sheep-tracks), or for the control of energy and natural resources, especially water but also timber and quarries. Occasionally, the tower is the only surviving element of a larger fortified unit which has been lost (as in S.Croce di Magliano or Pietrabbondante). In addition to the surviving artefacts, there were fortifications of which no trace remains, but which are recorded in the archive documents and ancient maps (for example the Zeppa tower, built in 1175 and later destroyed).