The system of tri-metalism which came to characterize Mughal coinage was introduced by Sher Shah. While the term rūpya had previously been used as a generic term for any silver coin, during his rule the termrūpiya came to be used as the name for a silver coin of a standard weight of 178 grains, which was the precursor of the modern rupee.[10] Rupee is today used as the national currency in India, Indonesia,Maldives, Mauritius, Nepal, Pakistan, Seychelles, Sri Lanka among other countries. Gold coins called theMohur weighing 169 grains and copper coins called Dam were also minted by his government.[10][15]Sher Shah built monuments including Rohtas Fort (now a UNESCO World Heritage Site in Pakistan), many structures in the Rohtasgarh Fort in Bihar, Sher Shah Suri Masjid, in Patna, built in 1540–1545 to commemorate his reign.Qila-i-Kuhna mosque, built by Sher Shah in 1541, at Purana Qila, Delhi, a Humayun citadel started in 1533, and later extended by him, along with the construction of Sher Mandal, an octagonal building inside the Purana Qila complex, which later served as the library of Humayun.Tarikh-i-Sher Shahi (History of Sher Shah), written by Abbas Khan Sarwani, a waqia-navis under later Mughal Emperor, Akbar around 1580, provides a detailed documentation about Sher Shah's administration.