Final answer:
Fallen arches, also known as flat feet or pes planus, occur due to the gradual lengthening of the ligaments that support the longitudinal arches in the feet.
Step-by-step explanation:
Fallen arches, also known as flat feet or pes planus, occur due to the gradual lengthening of the ligaments that support the longitudinal arches in the feet. This can happen in individuals who are overweight, have jobs that involve prolonged standing or walking, or engage in activities such as long-distance running. When the ligaments are stretched excessively or repeatedly, the supporting arches of the foot can become depressed or collapse, leading to fallen arches.