Actually, the sewer people mate with rats to make Ratmen, who then live in the sewers. So, there is more ratmen.
Because there's garbage, water, shelter, and safety in sewers. What more could they want?
RATS
yes
sewers
Rats, leaking sewers, dirty water, ankle deep rubbish and mud, and a lot more
Same as they do in a house or office
You can often find rats living in sewers, but that's not the only place they live. They can also live on the streets, especially dirty areas, in the country, in homes.. basically anywhere. Eww..
You can buy cheep fuzzy rats in the sewers
Garbage dumps, sewers and anywhere they can find shelter away from the eyes of people and other predators.
You can find these Hell Rats in the sewers in Varrock, You can find Varrock by exploring your map, have fun.
rats, garbage, poop
The sewers of London were built because at the time London was a stinking place were people were dying of preventable diseases. The father of modern railways talked the government into financing the building of sewers to remove the sewerage building up on the streets. As a bonus though when the sewers went in the scale of disease in ordinary Londoners dropped very quickly. No sewerage, no rats, no smell, no worries