There are two primary Celtic symbols that are associated with strength: the Dara Celtic Knot and the Ailm. Both symbols are connected to specific trees from which they derive the strength characteristic.
"Dara" comes from an Irish word for "oak tree," and its knotted design is a tribute to a strong oak's root system. Oak trees were sacred to the Celts and Druids, and they symbolized virtues, such as power, strength, wisdom, leadership and endurance. The Dara Knot is especially reflective of inner strength.
Ailm primarily symbolizes purity and wisdom, but its connection to ancient Celtic evergreen forests is representative of strength, endurance and resilience through adverse conditions.