Vastatio!

On a wider front, the Romans denied their enemies the means to keep sustained warfare. This was called vastatio. It was the systematic ravaging of an enemy territory. Crops were destroyed or stolen. Animals were slaughtered or taken. People were massacred or enslaved. The enemy's lands were demolished, denying his army any form of support. Sometimes these tactics were also used as a punitive method when barbarians crossed into Roman lands. This spread terror and acted as a deterrent. In the case of all-out war, the enemy was denied the means to survive a lengthy struggle.

"Roman Army Tactics." The Roman Empire. Web. 23 Mar. 2010. http://www.roman-empire.net/army/tactics.html.
FIRE. Digital image. Wikimedia Commons. Web. 20 Apr. 2010. http://upload.wikimedia.org/wikipedia/commons/2/2a/FIRE_01.JPG.