Possible on of the first (if not oldest) of defense types – a Watchtower was a simple structure (of varying heights), use by soldiers to observe enemy movements or to provide observations. Often, the term Watchtower and Observation Tower (or Post) is interchanged. The primary difference if that an Observation post is normally a more permanent structure. Most early Watchtowers were constructed of wood planking or tree logs (nailed or fastened together by rope or twine). As time progressed some were constructed of regional stone. Normally featuring a wide and flat platformed top (mostly enclosed). Some Watchtowers were purposely designed to be permanent structures (like The Tower of Hercules in Spain).Watchtowers could be attached to a fortifications perimeter defense system (as in a defensive Tower), or built many yards (or miles) from their support. As technology developed (with regards to communications) – so did The Watchtower. The Watchtower design was also incorporated into early (and still used) building facets of Prisons and other incarceration areas