In the United States, an architectural firm or architecture firm is a business that employs one or more licensed architects and practices the profession of architecture; while in South Africa, the United Kingdom, Ireland, Denmark and other countries, an architectural firm is a company that offers architectural services. History Architects (or master builders) have existed since early in recorded history. The earliest recorded architects include Imhotep (c. 2600 BCE) and Senemut (c. 1470 BCE). No writings exist to describe how these architects performed their work. However, as nobles it is reasonable to assume they had staffs of assistants and retainers to help refine and implement their work. The oldest surviving book on architecture, De architectura by the Roman architect Vitruvius describes the design and construction of towns, buildings, clocks, and machines, but provides no information about the organisation of the architect's assistants. It is generally accepted that throughout most of human history, most architects were wealthy individuals who derived their primary income from activities other than design and who practiced design as a part-time pursuit, employing assistants on a project-by-project basis. It was only in the 19th century that architecture began to be practiced as a full-time profession, when specific training and accreditation began to be offered. In the United States, Charles Bulfinch is the first American believed to have worked as a full-time professional architect. Henry Hobson Richardson may have been one of the first to have an established office and McKim, Mead, and White may have been among the first to resemble the large, modern architectural firm. The oldest active architecture firms in the United States are SmithGroup of Detroit, MI and Luckett and Farley of Louisville, KY, having both been founded in 1853. In the United Kingdom, Brierley Groom is the oldest continuing practice, having been founded in 1750 at York, England. They may be the oldest active architectural practice in the world. Licensure and legal form Architects may be licensed by individual states or provinces, as they are in Australia, Canada and the United States. Licensure is usually achieved by a combination of formal education, internship, and examinations. Although architects are licensed individually, state laws allow them to join together in various forms of business organisation. All states in the United States allow architects to form partnerships, most allow architects to form corporations or professional corporations, and some allow limited liability partnerships (LLPs) or limited liability