Joseon defended itself against ceaseless invasions. The country developed various excellent weapons besides bows and arrows. The armor worn by Joseon troops was made of layers of cotton sewn together. It was durable enough to protect the body from Japanese rifle bullets. The Bimongpo was a cannon that shot pot-shaped poison balls. There were also cannons that could fire five to ten balls in succession. They must have been a marvel at that time. It is said that the Japanese invaders were frightened at their thunderous sound and destructive power.