The Harmandir Sahib (informally referred to as the Golden Temple), the most prominent Sikh Gurdwara was built by the fifth Sikh guru, Guru Arjan, in the 16th Century. In 1604, Guru Arjan completed the Adi Granth, the holy scripture of Sikhism, and installed it in the Gurdwara. The present day Gurdwara was rebuilt in 1764 by Jassa Singh Ahluwalia with the help of other Sikh Misls. In the early nineteenth century, Maharaja Ranjit Singh secured the Punjab region from outside attack and covered the upper floors of the Gurdwara with gold, which gives it its distinctive appearance and its English name.