After the martyrdom of Guru Arjan, his son Guru Hargobind at age eleven became the sixth Guru of the Sikhs, and Sikhism dramatically evolved to become a political movement in addition to being religious. Guru Hargobind carried two swords, calling one spiritual and the other for temporal purpose (known as "mīrī" and "pīrī" in Sikhism). According to the Sikh tradition, Guru Arjan asked his son Hargobind to start a military tradition to protect the Sikh people and always keep himself surrounded by armed Sikhs. The building of an armed Sikh militia began with Guru Hargobind. Guru Hargobind was soon arrested by the Mughals and kept in jail in Gwalior. It is unclear how many years he served in prison, with different texts stating it to be between 2 and 12. He married three women, built a fort to defend Ramdaspur and created a formal court called Akal Takht, now the highest Khalsa Sikh religious authority.