Saturday's attack shows that Eta - Basque Homeland and Freedom - remains both intransigent and all but immune to counter-terrorist efforts by Madrid. Only weeks ago, the Spanish government said it was aware that Eta command structures remained intact.
Eta has planted a number of bombs against tourist targets in recent weeks, creating chaos and uncertainty in Spain's most important industry.
It is a diversion from its usual strategy. During 30 years of terrorism, Eta has usually gone for military or political targets: blowing up Civil Guard barracks, shooting or car-bombing politicians or military men linked to Basque security.
Even after Franco died in 1975, and the new democracy granted Basques the most generous degree of autonomy in Spain - indeed in Europe - Eta did not let up. It regarded Madrid's concessions as empty substitutes for full independence.
Only in 1987 did Eta aim at a "civilian" target. It bombed a supermarket in Barcelona, killing 21 and wounding 35. That attack bloodily interrupted attempts by the Socialist government to open up channels of dialogue with Eta.
The government's policy of rapprochement followed years of a "dirty war" during the early 1980s, when policemen and civil guardsmen were accused of murdering more than 20 Eta suspects. A clutch of former Socialist ministers are up before the Supreme Court, accused of masterminding these undercover hit-squads, and the scandal helped bring down Felipe Gonzalez's government in the March elections.
Jose Maria Aznar's conservative Popular Party came to power on a hardline anti-Eta platform. Mr Aznar narrowly escaped death in April last year when a huge Eta bomb blew his armoured car to smithereens. He walked calmly from the wreckage, unhurt. His coolness caused his popularity to soar, and within the year he was Prime Minister.
Eta followed that coup with a foiled plot to kill King Juan Carlos, a car-bomb that killed six in a working-class Madrid suburb and, during the election campaign, two important political assassinations. The second of these, that of the influential jurist, Francisco Tomas y Valiente, in his study at Madrid University, unleashed an outpouring of popular revulsion.
When Mr Aznar took power, his deeds were more conciliatory than his earlier words, in deference to conservative Basque nationalists whose support he needed. He appointed a respected Basque PP leader, Jaime Mayor Oreja, interior minister, who organised the return of some of the 500-plus Eta prisoners dispersed throughout Spain to jails nearer their homes. This was long an Eta demand, given clout by their kidnapping of a prison officer Jose Ortega Lara in January.
Last month Eta announced a week-long ceasefire, prompting Madrid for the first time in years to talk of opening indirect contacts. But Eta spurned the olive branch, so the government slammed the door. Its operating ability seems unimpaired, resistant to both blandishments and repression. The violence that has claimed more than 800 lives may be expected to go on, and Spain is braced for the next atrocity.
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