Sikhism originated in northern India in the 15th century through the teachings of Guru Nanak, who criticized aspects of both Hinduism and Islam. He taught that there is one God and all people are equal in God's eyes. The religion was further developed and scriptures were added by nine subsequent gurus over two centuries. Sikhism's holy book is the Guru Granth Sahib, and places of worship are called gurdwaras. Devout Sikhs follow the five Ks, including uncut hair and carrying a small sword. Sikhism faced opposition from Mughal rulers due to its challenges to Islamic practices.