The First Northern War happened around 1262-1263 and involved Nilfgaard's invasion and subsequent conquest of Cintra. Despite this, they ended up losing the war after the disastrous Battle of Sodden Hill.
Invasion of Cintra
In 1263, the Nilfgaardian Army, led by Menno Coehoorn, crossed the Amell Mountains through the Marnadal Stairs on the orders of Emperor Emhyr var Emreis. A full scale invasion of the north was launched and the Battle of Marnadal was fought against the Cintran Army at the mouth of the mountain pass, resulting in the defeat of the Cintrans and the death of their king Eist Tuirseach.
The army moved north through Erlenwald to the capital of Cintra where they sacked and slaughtered the entire city, with Queen Calanthe committing suicide, rather than be taken prisoner by the Nilfgaardians, and the death of most of the royal family.
Fighting in Upper Sodden
Attack on Lower Sodden
After burning Upper Sodden, the Nilfgaardian Army marched north and crossed the Yaruga into the region of Lower Sodden. They reached Sodden Hill and faced the armies of Redania, Temeria, Aedirn and Kaedwen, where the Battle of Sodden Hill, with over a hundred thousand participants, commenced. Over thirty thousand were killed, including thirteen northern mages, and the result ended in a sound Nilfgaardian defeat.
The Nilfgaardian Army retreated south, followed by the northern armies, until they crossed the Yaruga, and so across the river both armies reached a stalemate, and the Nilfgaardian Army marched into, and occupied, the captured lands of Cintra and Upper Sodden.