Gronder Field is a location in the east of the Adrestian Empire.
Known as the breadbasket of Fódlan, Gronder Field is a fertile area near the Airmid River that is well-suited for agriculture. It falls under the domain of House Bergliez. Gronder Field was also the site of the Battle of Gronder in Imperial Year 46, a notable clash in the War of Heroes in which the forces of the Adrestian Empire emerged victorious over the armies of Nemesis.
In Imperial Year 1180, Gronder Field was chosen for the Battle of the Eagle and Lion, a mock-battle and traditional contest of strength between the three student houses of Garreg Mach Monastery's Officers Academy. Depending on the house Byleth chose to lead, they will be the ones who wins the mock battle.
Five years later, war has erupted across Fódlan between the Adrestian Empire, Holy Kingdom of Faerghus, and Leicester Alliance. Just like the mock battle five years prior, the three factions lead by the house leaders of the Officer's Academy meet on Gronder Field. This time however, it is a real battle. The winner determined once again by the nation whom Byleth originally taught.
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Leading the Holy Kingdom of Faerghus alongside Dimitri, they are able to defeat the Empire and Alliance's forces, forcing both to retreat when Edelgard and Claude are defeated respectively. The former's defeat and subsequent escape from the battlefield enrages Dimitri who decides to follow her personally while the others go back. Dimitri fails to notice a young girl whom they took in at the Great Bride of Myrddin brandishing a sword who lands a deep wound. Just as she is about to land the final blow, Rodrigue takes the lethal strike, allowing Byleth to kill the girl.
Rodrigue's sacrifice causes Dimitri to realize the weight of his actions and how it had blinded him. While he still is bent on killing Edelgard, he has put that mission on hold in order to kill Cornelia in order to restore the Kingdom back under his control first.