Arminius was a son of Sigimerus, a chieftain of the GermanicCherusci tribe. He feared Roman conquest of Germany and so began studying them and their ways. He and his older brother Flavus enlisted with the German auxiliaries and helped put down a Pannonian uprising. This gave him first hand experience with Roman tactics and military organization.
Given his status among the Germans, Arminius was made an officer of the auxiliaries and given Roman citizenship without having served the full term of enlistment. He led a half cohort of auxiliaries into several battles and served with honor and distinction.
In AD 7, Chariomerus a distant kinsmen, arrived at the Roman encampment with a message from Sigimerus. Segestes, another Cherusci chieftain and the father of Thusnelda Arminius' betrothed, had broken off the engagement and betrothed her to another. Arminius was enraged at this slight to his honor but kept his wits. Rather than immediately return home, he sought out the senior Roman officer Titus Minucius Basilus. After explaining the situation and implying he would go home regardless, Basilus gave him permission to leave to resolve the situation.
Arminius and Chariomerus set off immediately. On the way Arminius thought about the matter. He did not want to start a blood feud with Segestes but still needed to avenge his honor. On arriving at his father's steading, he learned that Thusnelda had not yet wed Tudrus and continued to live at her father's steading. This simplified the situation and Arminius decided to elope with her.