You're looking for Redwall, the first book released in the Redwall series by Brian Jacques.
A young anthropomorphic mouse named Matthias is a novice monk at Redwall Abbey, where he was adopted as a young orphan, though he dreams of a life of adventure, inspired by the legends of Martin the Warrior, the founder of Redwall. One summer, Redwall Abbey is surrounded by the army of Cluny the Scourge, an infamously evil one-eyed rat. Matthias is guided by visions of Martin the Warrior, while the abbey inhabitants prepare the defense of their home against Cluny's impending attack. Matthias seeks Martin's famous sword, supposedly hidden somewhere within the abbey, helped particularly by Methuselah, an ancient and grizzled mouse who serves as Redwall's historian. Cluny, meanwhile, attempts to gain entrance to the abbey and murders a defector from his horde, Sela the fox. Sela's son, Chickenhound, seeks refuge at Redwall but ends up accidentally killing Methuselah after being caught stealing. Driven from the abbey, Chickenhound is maimed in the wilderness by the venomous adder Asmodeus Poisonteeth, a local terror in Mossflower Wood, the forest that surrounds the abbey.
Indeed, a tapestry plays into the clues Matthias follows:
The long tapestry showcases Martin the Warrior, wearing armor while leaning on his sword, surrounded by vermin, inclusive of foxes, rats, stoats, ferrets, weasels, and wildcats, who are fleeing him. While original accounts described Martin as located in the bottom right-hand corner, he was later described as appearing in the center of the tapestry. Behind it, Martin hid a riddle clue as to the location of his tomb.
