The largest tendon in the foot is the Achilles tendon, and the longest ligament in the foot is the plantar fascia, according to WakeMed Health and Hospitals. The Achilles tendon extends from the calf muscle to the heel and facilitates running, jumping and raising the body onto its toes.
The plantar fascia runs from the heel to the toe along the sole of the foot and forms the arch of the foot, states the Arthritis Foundation. This ligament helps to balance the body and gives the foot enough strength to walk by stretching and contracting. The plantar fascia is designed to handle a large amount of stress, but it can become damaged through repetitive activity, obesity or tight muscles, according to WakeMed Health and Hospitals.