For the third time in just over a year, hundreds of thousands of Spaniards answered a right-wing call to protest at the government's anti-terrorist policy.
They accuse the socialists of holding secret unconditional talks with Eta, and of giving in to terrorist demands.
Numbers for those who braved the rain and sleet on Saturday evening varied from police estimates of 110,000 to 1.4 million according to the organisers - a figure given to me even before the demonstration began.
Thousands had been brought in from around the country in special buses and trains to ensure a good turnout. The majority were the middle aged and middle class "fur and loden coat" brigade, waving Spanish flags, who made repeated calls for the resignation of prime minister José Luis Rodríguez Zapatero.
At the head of the march were two banners reading "For them, for us all" and "Not in my name" followed by three young women in wheelchair who lost limbs in Eta bombs. A short distance behind them were most of Spain's right-wing political leaders, including Popular Party (PP) leader Mariano Rajoy and the former prime minister José María Aznar, who said his government had held talks with Eta only after the terrorists had called a truce.
Just behind them was a banner written in English which read: "Zapatero surrenders to Eta."
Although there were no reports of violence, the mood was ugly and even menacing. I was repeatedly jostled and insulted as I tried to make my way through the masses to reach the other side of crowd. There were more attacks on the prime minister - the main target for their wrath - than on the terrorist organisation. Many demanded his resignation, and some called on him to "go and follow your grandfather".
Mr Zapatero's grandfather, a captain in the Republican army, was shot by Franco troops during Spain's civil war.
The demonstration was organised by the Association of Victims of Terrorism (AVT) , which is closely allied to the conservative PP. The organisation which represents the victims of the March 11th, 2005, Madrid train massacre and several other victims' movements refused to align themselves with the march.
AVT president Francísco José Alcaráz, who lost his brother in an Eta bomb attack, gave an inflammatory and angry address which was punctuated by shouts of "traitor, coward, resignation" from the crowd whenever Mr Zapatero was mentioned .
"How can we trust a prime minister who lies to us?" he asked.
"The government is selling out to Eta and getting nothing in return. He is selling our country because he wants to be seen as the man who ended Eta terrorism. Yes, we want peace, but not peace at any price. You cannot negotiate with the blood of our victims."
In Seville yesterday, Mr Zapatero referred indirectly to Saturday's demonstration by calling for loyalty from the opposition in the fight against terrorism.
"When I was leader of the opposition I gave PP my full support. I didn't do it to support Aznar, but I did so for the country and for liberty. Now, I call for their loyalty. Not for me, but for Spain, for democracy and for peace."