Västerås is situated at the mouth of the river Svartån by lake Mälaren (59°35'N 16°35'E). It's the sixth largest city in Sweden with around 125000 inhabitants, and is located approximately 110 km west of Stockholm.
The name is derived from Västra Aros, which means the western river mouth (Uppsala being the eastern one).
Around year 1000 was Västerås the second largest city in Sweden. In the 13th century it became one of the most important shipping harbours in Sweden shipping out iron and copper from the mining industry in the north. In the 16th century the silver found in Sala was also shipped via Västerås.
The castle was built in the 13th century, but was rebuilt by Gustav Vasa. He held several important diets here, of which the two most famous are the Västerås Recess (1527) which created the Lutheran State Church, and the diet of 1544 that made the Swedish throne hereditary. Gustav Vasa's eldest son, Erik XIV, was later held prisoner here by his younger brother Johan III, until his death by arsenic poisoning.
The cathedral dates back from the 13th century, but achieved it's current layout in the 15th century. Erik XIV is buried here.
In 1623, Johannes Rudbeckius created the first Gymnasium (modern equivalent is upper secondary school) in Sweden. Rudbeckianska Skolan is still used as an upper secondary school. For the trivia thirsty, the oldest Gymnasium in Sweden is in Lund, but as that was in Denmark at the time it wasn't the first Swedish one.
The next wave of importance to Västerås came during the industrial revolution. In 1891, a hydro-turbine station was built to generate electricity by the new company Allmänna Svenska Elektriska Aktiebolag, or ASEA for short, which in the 1980s merged with the Swiss firm Brown Bowery to become ABB. During the whole 20th century ASEA was more or less a synonym for Västerås.
Other industrial companies also contributed to the expansion of Västerås, like Nordiska Metallverken (Nordic Metal Works).
After World War II, the need for factory workers was huge, and the companies in Västerås started to actively recruit from abroad. They even sent buses down to southern Europe to recruit and relocate workers.
Today the manufacturing industry is not the sole bread winner, since retail, communications and services are becoming more and more dominant.
An example of that is the airport (IATA airport code VST), which used to be military, but now is a growing civilian airport. As a matter of fact, with its 2500 m long and 50 m wide runway, it's one of the few airports in Sweden that can accommodate a Concorde, something both British Airways and Air France have taken advantage of.