The Virgo interferometer is a large-scale scientific instrument near Pisa, Italy, for detecting gravitational waves. The detector is a Michelson interferometer, which can detect the minuscule length variations in its two 3 km (1.9 mi) arms induced by the passage of gravitational waves. The required precision is achieved using many systems to isolate it from the outside world, including keeping its mirrors and instrumentation in an ultra-high vacuum and suspending them using complex systems of pendula.