Igo is a kind of punishment carried out during the Nara and Heian periods to remove a criminal to another province.
It is the mandatory removal of a criminal sentenced to death for murder to another province to build a house in order to get out of trouble if this criminal at risk of revenge from parents, a brother, a sister etc. of the person he has been murdered.
According to 'the Hossoshiyosho,' if a gang of robbers commit a murder, the murderer and his boss shall be removed to a province. If the person murdered does not have any relations and therefore is not at any risk of being revenged, the criminal shall be affected to a group of technicians, Ryoko, Kanko, Kenin or Nuhi. However, if the criminal is a woman or if a Kenin or Nuhi of a another house is murdered, the criminal shall not be removed to another province. If a criminal to be removed is not removed or vice versa, a government official is sentenced to one-year penalty.