On this page of the Assassin's Creed Valhalla guide, you will find a detailed walkthrough of The Supply Line quest.
Eivor weakens the British forces by tracking and burning supply wagons. By weakening King Rhodri, he hopes to force him to start peace talks.
Rewards: 1700 XP.
Speak with the refugees
Refugees mentioned by Bishop Deorlaf can be found in a small camp by the river. One of the Anglo-Saxon men will tell you that the British are pushing their loot through the Dhustone Quarry.
Find Dhustone Quarry
You will find the quarry south of the refugee camp, behind the remains of the Hill Gate Remnants. To make it easier, we have marked the exact location on the picture above.
Find and burn the supplies
The quarry is well guarded, so you will have to deal with many guards during this task. It is also worthwhile to destroy the bell immediately, with the help of which soldiers can sound an alarm when the presence of Eivor is discovered.
Your main goal is to destroy the supply trucks in order to make the progress needed to complete the mission.
While exploring the quarry, also pay attention to the cages in which the warriors are kept, who can join your ranks. As areward for completing this mission you will receive 1 700 XP.