Wearing white tennis shoes and his trademark olive-green military garb, Castro marched at the head of a sea of demonstrators that passed the U.S. diplomatic mission on Havana's sea-front Malecon boulevard.
The march was billed by the ruling Communist Party as a protest against all U.S. "aggressions and crimes" since Castro's 1959 revolution ranging from the long-running economic embargo to this year's jailing of five Cuban agents, accused of spy-related charges.
"Down with the genocidal blockade! End the terrorism against Cuba! Free the heroes who defend their people from death!" chanted the marchers. Decked in the red-and-black colors of Castro's pre-revolutionary rebel group, they wore T-shirts with pictures of the agents jailed in Miami and waved flags.
The state-organized protest was the centerpiece of national celebrations for the 48th anniversary of Castro's July 26, 1953, attack on the Moncada Barracks.
Sixty-one of 160 attackers were killed and many of the rest, including Castro and his younger brother Raul, were jailed.
But the movement later regained strength and triumphed on New Year's Day 1959 after then-President Fulgencio Batista fled the country.
The 74-year-old Castro, whose June 23 fainting at a public rally fueled rumors over his health and speculation about who would succeed him, looked stern-faced but healthy. He did not address the crowd.
Castro marched briskly under the sun beside members of a visiting Iranian delegation including Hassan Khomeini, the grandson of the head of Iran's Islamic revolution, the late Ayatollah Ruhollah Khomeini and other Cuban leaders.
Castro waved a Cuban flag and chanted "Cuba, Yes! Yankees, No!" as he passed the imposing, seven-story U.S. building before continuing to walk a further two miles.
Castro had promised to be "more prudent" following his dizzy spell, which took place two hours into a speech under a blistering sun. But after a few days' rest, he was back, appearing near-daily at open-air rallies, state TV shows, conferences and meetings.
President Bush's public pledges to get tough on Castro by tightening implementation of the embargo have only fueled Castro's militancy, and was perhaps an underlying reason why he called for the largest march in Cuba's history.
Thursday, more than 10 percent of Cuba's total population of 11 million mobilized for the march. Havana came to a standstill as from long before dawn, hundreds of buses were out collecting groups of neighbors and workers from the capital and the surrounding province, for the meticulously-organized event.
Maps showed where each group should congegate down a three-mile stretch of the Malecon and intersecting roads. The march took more than three hours for everyone to pass, finishing around 11.15 a.m.
The march was the latest in about 20 months of constant anti-U.S. protests in Cuba several drawing up to 1 million people that began with the custody dispute over young shipwreck survivor Elian Gonzalez.
Some Cubans grumbled privately about having to attend the march to keep up appearances. And anti-Castro dissidents said the event was a transparent and costly attempt to shore up support and distract Cubans from their real daily problems.
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