The history of Sheffield, a city in South Yorkshire, England, can be traced back to the founding of a settlement in a clearing beside the River Sheaf in the second half of the 1st millennium AD. The area now known as Sheffield had seen human occupation since at least the last ice age, but significant growth in the settlements that are now incorporated into the city did not occur until the Industrial Revolution. Following the Norman conquest of England, Sheffield Castle was built to control the Saxon settlements and Sheffield developed into a small town, no larger than Sheffield City Centre. By the 14th century Sheffield was noted for the production of knives, and by 1600, overseen by the Company of Cutlers in Hallamshire, it had become the second centre of cutlery production in England after London. In the 1740s the crucible steel process was improved by Sheffield resident Benjamin Huntsman, allowing a much better production quality. At about the same time, Sheffield plate, a form of silver plating, was invented. The associated industries led to the rapid growth of Sheffield; the town was incorporated as a borough in 1843 and granted a city charter in 1893. Sheffield remained a major industrial city throughout the first half of the 20th century, but the downturn in world trade following the 1973 oil crisis, technological improvements and economies of scale, and a wide-reaching restructuring of steel production throughout the European Economic Community led to the closure of many of the steelworks from the early 1970s onward. Urban and economic regeneration schemes began in the late 1980s to diversify the city's economy. Sheffield is now a centre for banking and insurance functions with HSBC, Santander and Aviva having regional offices in the city. The city has also attracted digital start-ups, with 25,000 now employed in the digital sector. Early history The earliest known evidence of human occupation in the Sheffield area was found at Creswell Crags in Derbyshire to the east of the city. Artefacts and rock art found in caves at this site have been dated by archaeologists to the late Upper Palaeolithic period, at least 12,800 years ago. Other prehistoric remains found in Sheffield include a Mesolithic "house"—a circle of stones in the shape of a hut-base dating to around 8000 BC, found at Deepcar, in the northern part of the city. This has been ascribed to the Maglemosian culture.(). The