The bank is based in Frankfurt, the largest financial centre in the Eurozone. Its location in the city is fixed by the Amsterdam Treaty. The bank moved to new purpose-built headquarters in 2014 which were designed a Vienna-based architectural office named Coop Himmelbau. The building is approximately 180 metres (591 ft) tall and will be accompanied with other secondary buildings on a landscaped site on the site of the former wholesale market in the eastern part of Frankfurt am Main. The main construction began in October 2008, and it was expected that the building will become an architectural symbol for Europe. While it was designed to accommodate double the number of staff who operate in the former Eurotower, that building has been retained since the ECB took responsibility for banking supervision and more space was hence required.
Try to answer this question if possible (otherwise reply "unanswerable"): What decided where the bank was to be located?
Amsterdam Treaty