Smoke hung heavily over this hilly city, broken by flickering flames, when I mustered my courage, plunged into the crowd and brought down my bright-green hammer on a stranger's head.
"Bom Sao Joao!" - "Happy St John!" - the grey-haired man beamed as he hit me back, the circus-like squeaks of our soft plastic hammers inducting me into the celebration of Porto's patron saint.
All around, tens of thousands of similarly armed revellers were indulging in other local St John rituals - devouring sardines off the smoky outdoor grills and sending mini papier mache hot-air balloons heavenward.
From late Northern Hemisphere spring to autumn, virtually all Spanish and Portuguese capitals, towns and hamlets turn into moveable feasts in honour of their patrons.
The multi-day, multi-generational revelries provide occasions to experience the distinct cultures together with locals at their proudest and perkiest. Here are some details on four Iberian holy days I've enjoyed.
MADRID'S SAN ISIDRO
Giant puppet parade, folk street dances, procession and High Mass, open-air flamenco concert, fireworks and a bullfight - I presented my characteristically over-packed advance programme to madrileno friends.
They seemed puzzled.
"Isn't this what you do for San Isidro?" I asked a bit defensively.
"Mostly we just party," was the rather apologetic response - which I'm sure pleases St Isidore the Labourer (and his wife, whose statue is also carried in the procession).
I still thrilled, together with wide-eyed kids, as the gigantes y cabezudos - four-metre-high puppets - paraded through the historic Puerta del Sol and Plaza de la Villa. I hummed along as older couples danced the chotis near the Royal Palace and as a flamenco performance vibrated through the stage-perfect Plaza Mayor.
With friends from New York and Rome, we squeezed among ebullient throngs of bullfighting fans at the landmark Las Ventas arena, cheering and recoiling as world champions El Fandi and Fandino pirouetted around feisty bulls.
But the last afternoon even I relented and, skipping the state fair-like madness at la Pradera, simply chilled with the holiday-wearied crowds among the shady lawns and rose garden of El Retiro park.
GRANADA'S CORPUS CHRISTI
Bullfights, dances and a buzzing fair also mark the Corpus Christi celebration in this gorgeous southern city, full of monuments from when it was the last Islamic stronghold to fall to Spain's Catholic kings.
But the atmosphere of the signal event could not be more solemn - appropriately enough, since the celebration here dates from those reconquista days and centres on the Eucharist carried in procession.
After a packed Mass, I watched as dignitary after dignitary filed out of the triumphantly grand cathedral.
Black and white lace mantillas flowed high from the women's immobile coiffed heads, as did fluffy plumes from the helmets of civilian and military authorities.
In the narrow city streets draped in flags and shawls, a hush followed the gigantic flower-covered silver float, borne by a couple of dozen men, carrying the consecrated host.
Then someone in the crowd would yell "viva!" and the faithful would cheer and applaud, as people watching from their apartments showered rose petals.
BELORADO'S FERIA ALFONSINA
Incense and fairy floss also wafted through this village, on the historic pilgrimage route Camino de Santiago in northern Spain, its main square framed by the ruins of its medieval castle and a couple of fake arches set up for the occasion.
It seemed that the whole population, in elaborate costumes, participated in re-enacting the day nearly 900 years ago when King Alfonso I decreed that a feria should be celebrated here - the first official one in Spain, or so the narrator said.
Peasants, princes and bishops watched soldiers perform dangerous balancing acts with swords until the grey-bearded king took off on a trotting white horse - only his majesty's wireless microphone hinting at the 21st century.
PORTO'S SAO JOAO
Aside from the elaborate creches with St John figurines in many courtyards, religion is hardly on display during the all-night party or the next day, when the protagonist is this northern Portuguese city's namesake wine.
A regatta of rabelos, the boats that once transported barrels, sails from the Atlantic mouth of the Douro River to the historic centre, crowded with blue tile-covered buildings, port flowing in profusion among the fans well before noon.
Knowing this, I secretly welcomed my friends' mournful announcement, a couple of hours
past the midnight fireworks, that we should begin to walk home because their 4-year-old son was tired.
Swinging the last hits with my squeaking martelo among jubilant festa-goers, I thought again that few know how to party like Iberian saint celebrants.
IBERIAN HOLY DAYS
The festivals run for several days around specific dates:
• Madrid's San Isidro: May 15
• Granada's Corpus Christi: May 15
• Porto's Sao Joao: June 23-24
• Belorado's Feria Alfonsina: the first weekend in June.
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