What is the history of a Rottweiler?

What were Rottweilers originally bread for? Were they bread for,hunting dogs,farm dogs,rescue dogs etc..I was wondering because every one I know that owns a Rottweiler says they are the best loyal dogs they have ever had.I own a rottweiler as well and she is 11 yrs old and I heard their life expectancy is only 10.She seems to be on overall good health accept she is slowly loosing her vision and has some pain in her hips.I'm hoping my precious dog lives for another 4 to 5 yrs.but I don't know much about the bread.There are others who say that they aren't a good breed to own ,because of their temperament,and they could turn on you at any time.Well I never had a problem with my dog having behavior issues.