WHO ARE ETA?: Euskadi Ta Askatasuna - Basque Country and Liberty - was founded in 1959 as a student opposition group during Spain's Franco dictatorship.
What do they want?
Independence for seven Basque provinces, four in Spain, three in France; also several varieties of socialist Utopia in the course of its history.
Their first killing?
A civil guard in 1968; the Eta member who killed him was shot by other civil guards the next day, giving Eta its first victim and first "martyr" in 24 hours.
Early claim to infamy?
The murder of Admiral Luis Carrero Blanco, Franco's prime minister, in 1973. This arguably removed an obstacle to Spain's subsequent transition to democracy, and gave the group a short-lived, romantic, legitimacy in the eyes of many anti-Francoists.
As Spain embraced democracy in the late 1970s, Eta escalated its terrorism, killing 91 people in 1980, the highest number of victims it has claimed to date.
Why?
Eta says that the Basque Country's unique language cultural heritage will vanish unless it has total independence, despite the fact that three of the Spanish provinces already enjoy more autonomy than any other EU region.
What do Basques think?
They are divided. About half of them would certainly like some form of self-determination. Most of these vote for the PNV, and about 15 per cent have generally indicated support for Eta by voting for its political wing, Batasuna. The remaining Basques are happy with the present autonomy arrangements.
Eta's worst atrocity.
Bombing of a Hipercor supermarket in Barcelona, 1987, in which 21 people died.
Did Eta target civilians in the past?
Possibly, not deliberately, though its operations showed contempt for civilian lives on many occasions.
How does Madrid respond to Eta?
In the 1980s, Socialist Party administrations were implicated in the use of state terrorism, which predictably boosted ETA support among Basque sympathisers. The current conservative government insists that it stays within the law, but implements a tough police and judicial policy.
What about the Basque peace process?
Influenced by events in Ireland, non-violent nationalists and Eta supporters formed a common front in 1998, followed by an Eta ceasefire.
Why didn't that work?
Madrid insisted there was nothing to negotiate, and was slow to make concessions on prisoners. Eta did not seem willing to make any concessions at all, and ended its ceasefire in 1999, with a series of "soft target" killings that shocked even many of its supporters.
How did its supporters react?
Half of them switched from Batasuna to the non-violent nationalists of the PNV.
How did Madrid react?
By banning Batasuna, and engaging in confrontational politics with the PNV. The latter launched a campaign for a referendum on self-determination, which polarised matters further.
So how did things stand until yesterday?
The political atmosphere between Madrid and Basque nationalists was more poisonous than ever, but Eta appeared to be on the point of collapse.
Paddy Woodworth