In 83 b.c. L. Cornelius Sulla invaded Italy to face his political enemies in civil war. From Brundisium he moved quickly into Campania, defeated C. Norbanus near Capua, won over the army of the other consul, L. Scipio, near Teanum Sidicinum, and advanced some way northwards—possibly to Aquinum in the middle Liris basin. There followed a lengthy pause in operations, and a very hard winter.
Next year, Sulla beat the illegally youthful consul C. Marius somewhere in the upper valley of the Trerus (the Sacco of today), and pursued him and his routed forces into Praeneste, which he proceeded to besiege. It was vital not to leave this immensely strong site, which dominates eastern Latium and with it one of the through passages from Rome to Campania, in enemy hands. Marius' considerable forces had to be neutralised, lest they endanger Sulla's rear as he pressed on north of Rome against Carbo in Etruria, lest they effect a junction with Carbo, or lest they provide a focal point (and a base) for Italic peoples not prepared to accept Sulla, and likely to offer Marius ready recruits, if he were left unhindered. Besides, the town itself was anti-Sullan—and prepared beforehand for such a siege, it seems.