Eta has begun the process of handing over its remaining weapons, formally ending the last remaining insurgency in Europe.
At a ceremony in the southern French city of Bayonne, an inventory of weapons, and their locations, was passed to the judicial authorities.
The Basque militant group killed more than 800 people and wounded thousands in more than 40 years of violence.
Eta declared a ceasefire in 2011 but did not disarm.
The group’s goal was to create an independent Basque state out of territory in south-west France and northern Spain.
France and Spain refuse to negotiate with Eta, which is on the EU blacklist of terrorist organizations.
The Bayonne ceremony took place in the presence of the local mayor, an Italian archbishop and an Irish priest, and civil society representatives.
The Chairman of the International Verification Commission, Ram Manikkalingam, said he hoped this important step would help consolidate peace in the Basque region.
Speaking on April 7, Spanish government spokesman Inigo Mendez de Vigo said Eta “will get nothing from a democratic state like Spain”.
Inigo Mendez de Vigo demanded that Eta not only disarm, but also clarify who carried out past its attacks.
In recent years, police in France and Spain have put Eta under severe pressure, arresting hundreds of militants, including leadership figures, and seizing many of its weapons.
Eta was set up more than 50 years ago in the era of Spanish dictator General Franco. Its first known killing was in 1968, when a secret police chief, Meliton Manzanas, was shot dead in the Basque city of San Sebastian.
In 2014 the International Verification Commission of inspectors said Eta had put some of its weapons out of action, but the Spanish government dismissed the move as “theatrical”.