Leeds is a city in the metropolitan borough of Leeds, in the county of West Yorkshire, England. The city lies within the United Kingdom's fourth-most populous urban area, with a population of 2.6 million. Leeds was a small manorial borough in the 13th century, and in the 17th and 18th centuries it became a major centre for the production and trading of wool, and in the Industrial Revolution a major mill town; wool was still the dominant industry, but flax, engineering, iron foundries, printing, and other industries were also important. From being a market town in the valley of the River Aire in the 16th century, Leeds expanded and absorbed the surrounding villages to become a populous urban centre by the mid-20th century. Leeds has one of the most diverse economies of the all the UK’s main employment centres and has seen the fastest rate of private-sector jobs growth of any UK city. It also has the highest ratio of private to public sector jobs of all the UK's Core Cities, with 77% of its workforce working in the private sector. Leeds has the third-largest jobs total by local authority area, with 480,000 in employment and self-employment at the beginning of 2015. Leeds is ranked as a gamma world city by the Globalization and World Cities Research Network. Leeds is the cultural, financial and commercial heart of the West Yorkshire Urban Area. Leeds is served by four universities, and has the fourth largest student population in the country and the country's fourth largest urban economy. Today, Leeds has become the largest legal and financial centre, outside London with the financial and insurance services industry worth £13 billion to the city's economy. The Finance and business service sector account for 38% of total output with more than 30 national and international banks located in the city, including an office of the Bank of England. Leeds is also the UK's third-largest manufacturing centre with around 1,800 firms and 39,000 employees.