Yorkshire is a historic county of northern England and the largest in Great Britain. Because of its great size, over time functions have increasingly been undertaken by its subdivisions, which have been subject to periodic reform. Throughout these changes Yorkshire has continued to function as a recognised territory and cultural region. The name is familiar and well-understood across the United Kingdom and is in common use, featuring in the title of current areas of civil administration such as Yorkshire and the Humber. Throughout much of history, Yorkshire has played a prominent role in Great Britain. The Brigantes, who were the largest Celtic Briton tribe held it as their heartland. The Romans made Eboracum, later to be named York, from which the county derives its name, the capital of Britannia Inferior, one of the provinces of Roman Britain. The area was an independent Viking kingdom known as Jórvík for around a century, before being taken by England. Most of the modern day large cities were founded during the Norman period. The county covered just under 6,000 square miles (15,000 km²) in 1831 and the modern day Yorkshire and the Humber region has a population of around five million. Yorkshire is widely considered to be the greenest area in England, due to both the vast rural countryside of the Yorkshire Dales, North York Moors and some of the major cities, this has led to Yorkshire being nicknamed God's Own County. The emblem of Yorkshire is the White Rose of the House of York, the most common flag representative of Yorkshire is the White Rose on a dark blue background. Yorkshire Day, held on August 1, is a celebration of the general culture of Yorkshire, ranging from its history to its own language. More on Yorkshire