Battle of the Zel system

This battle took place on the planet of Zeltros in 3,962 BBY as part of the Mandalorian Wars, a conflict between the Galactic Republic and Mandalorian Neo-Crusaders. The battle took place because the Mandalorians campaigned to take control of the Core World of Duro. Called "Mandalorian Triumph," this charge, which was ultimately successful, took the Mandalorian forces from their territory through the planet of Ambria and to Zeltros. Once the Mandalorians had taken this world, they took the planet of Commenor, then Quellor before moving on to the planet of Exodeen, staging their capture of Duro.

Behind the scenes
The Battle of Zeltros is only referenced once in The Essential Atlas. The battle was marked on the galactic map showing the battles of the Mandalorian Wars rather than in prose.