A turbine square is a square shape with the streets flaring out of the square walls. The streets are not straight across the square.
The principle of the turbine square was designed by the Austrian urbanist Camillo Sitte, who sought optically closed urban squares, despite the wider streets needed for busy urban traffic in the second half of the nineteenth century. The theories of Camillo Sitte were probably introduced in the Netherlands by the architect and urban architect H.P. Berlage, strongly influenced by him, and the designer of Mercator Square. A beautiful example of a turbine square is the Main Square Square.
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