The so called First Battle of the Fields of Streges was a battle between the armies of the Dread Empire of Praes and the Kingdom of Callow, taking place around sixty years before the start of the story. It was a crushing defeat for the newly crowned Dread Emperor Nefarious and resulted in him not leaving the Tower for the rest of his reign, as well as the death of the then active Black Knight, and was the impetus for Amadeus of the Green Stretch to eventually become the Squire. The name is technically a misnomer, since the fields have seen "a hundred battles between Callow and Praes", but became common in the years after The Conquest as an easy way to differentiate it from the more recent battle at the same place.
While the Wizard of the West Theodore Langman faced off with Emperor Nefarious, Good King Robert met the Praesi army with a staggered approach of foot soldiers anchored by heavy cavalry. The Legions of Terror, having not yet gone through the Reforms, poured forward recklessly and were crushed between the charging cavalry and the flanking infantry. The very same tactic was used against an onrushing devil horde by General Juniper of the Fifteenth Legion in the Second Battle of Liesse.
As shown in the article on Amadeus of the Green Stretch, the battle took place sometime between 1261 and 1271 a.D.