What did the warrior strap on his back?

The text below is part of the Japanese tale “My Lord Bag of Rice”:

“Long, long ago there lived in Japan a brave warrior known to all as Tawara Toda or “My Lord Bag of Rice”. His true name was Fujiwara Hidesato and there is a very interesting story of how he came to change his name. One day he went out in search of adventures because he had the nature of a warrior and could not bear to be idle. So he picked up his two swords, took his huge bow, which was much taller than himself, in his hand, strapped his quiver on his back and started out.

He had not gone far when he came to the bridge of Seta-no-Karashi crossing one end of the beautiful Lake Biwa. As soon as he stepped on the bridge, he saw lying right across his path a huge serpent-dragon. Its body was so big that it looked like the trunk of a large pine tree and it took up the whole width of the bridge. One of its huge claws rested on the parapet of one side of the bridge while its tail lay right against the other. The monster seemed to be asleep, and as it breathed, fire and smoke came out of its nostrils.

At first, Hidesato could not help feeling alarmed at the sight of this horrible reptile lying in his path, for he must either turn back or walk right over its body.”