The bubonic plague (Black Death) was a disease which brought death to most parts of Asia, North Africa and Europe. The first outbreak was recorded in 1331 in China.
The plague started as a bloody swelling in the armpit or groin and quickly invaded the whole body. It was highly contagious and killed millions of people.
The infection probably began on the steppes, the grassy plains of Asia. It was carried by fleas which lived in the fur of the black rat.
The rats lived close to humans and thus the disease spread rapidly. Corpses were left out in the road for people to collect, thus causing the disease to spread even further.