After centuries of stagnation and decline, Amsterdam flourished again beginning in 1850. Tens of thousands of newcomers found work in the city. All these people also had to live somewhere, but the municipality was not prepared for this. After years of inaction, an ambitious expansion plan was launched in 1877: property developers were allowed to build homes in the polders around the city. They did so at an unprecedented rate: between 1877 and 1940, as many as 135,000 public housing units were built, more than 75 percent of which were commissioned by project developers. These property developers played a key role in the development of Amsterdam, but as yet almost nothing is known about their activities. In the book Speculators and Revolutionary Builders, Rens Smid uses careful archive research to show that mortgage banks were not the money wolves who charged sky-high interest rates and imposed repayment terms that were far too short. The price development of building land was moderate. The supply of land was plentiful, and workers and small middlemen had limited purchasing power. Without private project development, the rapid economic and spatial development of Amsterdam during this crucial period would not have been possible.