The Jantar Mantar in Jaipur is one of five observatories built by Maharaja Jai Singh II of Jaipur between 1724 ans 1735.
A Jantar Mantar is an assembly of stone-built astronomical instruments, many of which were (partly) reconstructed or rebuilt in the 20th century.
One model for this was Ulugh Beg's observatory in Samarkand from the 15th century
