Gelsenkirchen is a city in the North Rhine-Westphalia state of Germany. It is located in the northern part of the Ruhr area. Its population in 2015 was c. 260,000. Gelsenkirchen was first documented in 1150, but it remained a tiny village until the 19th century, when the Industrial Revolution led to the growth of the entire area. In 1840, when the mining of coal began, 6,000 inhabitants lived in Gelsenkirchen; in 1900 the population had increased to 138,000. In the early 20th century, Gelsenkirchen was the most important coal mining town in Europe. It was called the "city of a thousand fires" for the flames of mine gasses flaring at night. In 1928, Gelsenkirchen was merged with the adjoining cities of Buer and Horst|de|3=Gelsenkirchen-Horst}}. The city bore the name Gelsenkirchen-Buer, until it was renamed Gelsenkirchen in 1930. During the Nazi era Gelsenkirchen remained a centre of coal production and oil refining, and for this reason it was bombed in Allied air raids during World War II. There are no longer colliers in Gelsenkirchen with the city searching for a new image, having been hit for decades with one of the highest unemployment rates in Germany. Today Germanys largest solar power plant is located in the city. In Gelsenkirchen-Scholven there is a coal-fired power station with the tallest chimneys in Germany. Gelsenkirchen is home of the famous football club Schalke 04, which is named after the borough Schalke, while the clubs stadium, the Veltins-Arena, is located in the borough of Erle.