Defining "Pitbull" and Where "Pitbulls" Come From:

The term "Pitbull" doesn't always mean one particular breed of dog. Generally it used to describe a strong, muscular dog. It is a social construct that encompasses breeds lumped into the catagory, "Pitbull":

1. American Pit Bull Terrier (UKC)
2. American Staffordshire Terrier (AKC)
3. (English) Staffordshire Terrier
4. Bull Terrier
5. English and American Bulldog
6. Argentinian Dogo (Mastiff)
7. Or any Bully-breed hybrid (generally those mixed with a larger breed such as a sheperd, retriever, etc.)

Where "Pitbulls" come from: 

Ancient Times:

"Pitbulls" as well as all bully-breeds are believed to ascend from the early Greek-Mastiff type dogs called, "Molossians". These would resemble closely to today's Mastiff breed.

The Molossians were imported into the realm of fighting throughout the Roman Empire. These large dogs were used also as soldiers in armies. One Egyptian pharaoh "kept a retinue2,000 fighting dogs in his army" (Gallagher 6). They were a form of entertainment in which these large dogs would fight another creature ranging from a human to an elephant.

During the Middle Ages when mechancial armaments and weapons caused these dogs to become obsolete, their jobs transfered to being guard dogs and hunters of bears, wolves and other raiders.

Bear and Bull Baiting

Originating in Germany, "bullenbeiser"(bull biter) and "barenbeiser"(bear biter) became a popular sport throughout Europe. People would gather to watch these mastiffs attack a chained bull or bear. The bulls horns "frequently gored the dogs or tossed them up toe 50 feet in the air" (Gallagher 7). The "quicker dogs, more successful in surviving these encounters, soon began to replace the larger, slower mastiffs in battling bulls and the occastional bear" (Stahlkuppe 22). This would create a "bulldog" breed that was more agile ans stronger to fight against larger animals. Merchants would spread these dogs around Europe.

Outcault, Richard F. "Buster Brown, Tige and the Bull". Cupples & Leon Co. New York. c. 1907.   Buster Brown was a comic strip that was created by Richard Outcault in the early 1900s. Buster Brown was the commerical mascot for Buster Brown Shoes. His companion, Tige (which is short for Tiger), was modeled after Outcault's own dog, an American Pit Bull Terrier.   In this comic book cover, by Outcault, it depicts Buster with an old camera, looking at Tige, who is latched onto the nose of a rearing bull. The picture shows the nature of the dog as it is depicted in the past century. Buster Brown generally is the one getting into schemes where Tige is actting as his voice of reason. This picture shows that Tige is battling a bull of much greater proportions, which might not be his greatest idea. Seeing how these dogs were originally bred for bull and bear baiting, even though Tige was Buster's voice of reason, he is apparently drawing upon a stereotypical instinct of the "breed". There is a level of fear that this picture represents. Buster's body is in a frantic position and the viewer might wonder what the next frame might looks like. Does Tige escape unharmed?

Bull-and-Terrier Theory

The bull-and-terrier is another suggested origin of the American Pit Bull Terrier. It is a cross between a Bulldog ( the non-pug-like ones) and a Terrier.