PIANO, PIANO! But there was no denying the adrenaline surge of my first peloton. I was part of a great dragon of illumined cyclists six riders abreast, the head of the beast perpetually disappearing around the bend ahead, the tail still flowing out of the piazza behind. We made a hissing sound like gentle surf, spokes whirring, tires snicking smooth wet pavement. The first bit was all descent, a ten-kilometer/six-mile coast south toward Siena, but cold! I shivered so hard my whole bike shook. My fingers burned, then went numb, so I alternated hands on the bars, shoving the other into my armpit to restore sensation. I was passed by a lot of riders with gloves.

At last an official with a flashlight appeared, waving us off the highway and onto the first section of strade bianche. The limestone seemed to glow in the dark. It crackled, was both grabby and suddenly not. The workout brought blessed warmth. Over this first long, undulating climb, the pack spread out single-file to a long, thin thread. By the time the sky showed pink, I was sweating contentedly, and with the first red sliver of old Sol upon the horizon, the countryside erupted with shotgun blasts, the gentry out shooting birds.

Had I done the math at the first control point, the 40-kilometer/25-mile mark, I might've noted I was kind of dogging it. But I was happily gobbling more pastries and grapes and slurping hot coffee. Besides, there were at least a hundred of us! I was right in the thick of things. Too many minutes later, I was back at it in high spirits.

But soon the first of the 15 percent gravel climbs rose up like the pale brow of Moby-Dick. It looked insurmountable, like you'd just bounce off. I shifted to my lowest gear and hit it out of the saddle, surging all the way up on sheer audacity. But the next section was even steeper. (Some hit 18 percent.) A few cranks into it, I spun out, spitting gravel. So I walked.

At the top of every hill was a prize: the ruins of a castle of the Guelfs and Ghibellines, a 14th-century fortress, a grand villa commanding a noble view of vineyards and olive orchards. Then came the tunnel vision of a roller-coaster descent, every bit as demanding as the climb and much more dangerous. At the checkpoint, a sixty-something South African on a mint '63 Raleigh described the course as "very sporting."

"Quite," I said around a mouthful of salame sandwich.

After a crash at zero kilometers per hour that bloodied a knee and an elbow, I developed a strategy: Stand up, sit down, spin out, get off and hike. At a forced march I could nearly keep up with the young dudes with cannonball calves and 27 speeds grinding out the steepest sections. But of those who never walked, there were also riders much older than me, pedaling bikes even older than themselves. Talk about heroic. A great many featured only one gear, and it was no granny.