Once on his pilgrimage to visit sacred places Arjuna met Hanuman at Rameswaram. Arjuna over-confident about himself said, "Rama need not have asked the monkeys to build a bridge. If I were here, I would have built a bridge with arrows." "A bridge of your arrows! Leave alone the Vanara army, it will crumble under my feet" replied Hanuman. Well, it developed into a challenge. It was decided that Arjuna should erect a bridge with his arrows and Hanuman should walk on it. If the bridge collapsed, Arjuna should jump into fire; otherwise, Hanuman must adorn Arjuna's banner.
Arjuna built a bridge with his arrows. No sooner did Hanuman set one foot on it than it broke into pieces. Arjuna got ready to jump into the fire. Just then, Shri Krishna reached the place. He asked them to repeat their performances. When Arjuna erected the arrow-bridge, Krishna touched the bridge with his divine hands as if to test it. Then when Hanuman danced on it heavily, it did not even shake. Hanuman was shocked and then realised that Krisha is none other than Rama. Hanuman kept his word and entered Arjuna's banner.
Name of Arjuna
Arjuna's special chariot is always marked with the picture of Hanuman, and therefore his name is also Kapidhvaja. (Kapi means Hanuman, and dhvaja