The history of the place is kind of mysterious. It is not clear what's the real meaning/origin of the name of the city. it is believed that it was created by the Tuareg around the 11th century, and over the years became a major center of trade and learning until was ransacked by the Morokkans in 1591.
If you go there, visit the market, take a camel ride, go to the swordsmiths and buy a proper Tuareg sword. Walking around the city you'll see the houses where the first European travelers stayed.
You can get there either by plane or by sailing on the Niger (from Bamako or Mopti). I recommend sailing. It takes 2-3 days, you get to sleep on the river banks, you get to see zebus and hyppos. It's quite nice