Switzerland has one of Europes oldest green roofs, created in 1914 at the Moos lake water-treatment plant, Wollishofen, Zürich.  Its filter tanks have  of flat concrete roofs.  To keep the interior cool and prevent bacterial growth in the filtration beds, a drainage layer of gravel and a  layer of soil was spread over the roofs, which had been waterproofed with asphalt.  A meadow developed from seeds already present in the soil; it is now a haven for many plant species, some of which are now otherwise extinct in the district, most notably 6,000 Orchis morio (green-winged orchid).  More recent Swiss examples can be found at Klinikum 1 and Klinikum 2, the Cantonal Hospitals of Basel, and the Sihlpost platform at Zürichs main railway station.