In 154 BC., the city of Segeda (Mara, Zaragoza) started to widen its walls and gain “importance and strength” to the detriment of Titus neighbours, for this reason Rome accused it to breach the Treaty of Graco (179 BC.), declaring war. Rome sent at the head of Nobilior an army of 30,000 soldiers. Segenda people abandoned their homes and called for help Numantia, where they were welcomed as allies and friends. So started Celtiberian wars leaded by Numantia.
In Rome there was other problem. The Roman year started in Ides of March (on the 15th of March). This day, they elected official charges and consuls to make war in Hispania. But when they arrived it was June losing in this way a lot of time to make war (they make war in spring and summer).
For this reason Senate was obliged to change the beginning of year to Kalends of January (on the 1st of January). Inheriting Roman calendar, the fact that our year starts in January is a direct consequence of Celtiberian wars.