Consequently, specific types of horse developed, many of which have no modern equivalent. While an understanding of modern horse breeds and equestrianism is vital for any analysis of the medieval horse, researchers also need to consider documentary (both written and pictorial) and archaeological evidence. Consequently, the assumptions and theories developed by historians are not definitive, and debate still rages on many issues, such as the breeding or size of the horse, and a number of sources must be consulted in order to understand the breadth of the subject.