The skirmishing formation was a widely spaced line of troops, as opposed to the tighter packed battle ranks typical of Roman legionaries. Every second man in the line stepped forward a few paces, essentially doubling the amount of ranks. It allowed for greater mobility and found many uses in the tactical handbooks of Roman generals.
"Roman Army Tactics." The Roman Empire. Web. 23 Mar. 2010. http://www.roman-empire.net/army/tactics.html.
Skirmishing Formation. Digital image. Roman-Empire.net. Web. 1 Apr. 2010. http://www.roman-empire.net/army/skirmishing.html.