This trail is but a fraction of a vast 14,000-mile network that, in the words of one dumbstruck Spanish conquistador, "excels the constructions of Egypt and the monuments of Rome." More numbing still, no one will ever really know how this vast web of trails and the cities and temples they linked were constructed. The Incas didn't keep records, and their Spanish conquerors, intent on wiping out all reminders of Inca presence, wouldn't have left them intact if they did.

What is known is this: An Inca messenger, chasqui in the Quechua language, probably ran this very trail 500 years ago, headed, maybe, as we are, to Wayllabamba, or Ollantaytambo, or perhaps the legendary city of Machu Picchu. And he did so a lot faster than I.

We are here, seventeen of us, to enjoy the natural splendors of Peru, explore the local culture, and learn about Peru's Inca past. This is not unusual. Since the government has largely quashed its number-one public-relations stumbling block (the now-subdued Shining Path terrorist group), tourists these days are coming to Peru in droves, most of them making the pilgrimage to Machu Picchu, the lost city of the Incas.

But these visitors generally travel by bus, helicopter, or train. Our itinerary calls for us to run, and not because we are late for our bus. We have signed on to run the Inca Trail to Machu Picchu and beyond - along wind-swept rivers, through damp cloud forests, up and over blustery mountain passes - because we want to.

At least running is what my new friends came to do.

As Bob Graham, a fifty-six-year-old emergency-room doctor from Connecticut, tells me, "Running is a great way to explore a place. You see things you wouldn't normally see."

Like everyone else's rump disappearing up the trail. Only a few days into the trip, we have already established a pecking order, and I am right at the back. Not that anyone cares. My fellow runners - and, unlike me, most of them really are runners - are distinguished less by their impressive athletic accomplishments - marathons, 100-mile races, a rim-to-rim-and-back run of the Grand Canyon with only two pretzels' worth of supplies - than by their plucky mind-set.

Our first night in Cuzco, our starting point before we set out on our run, I sat next to Amanda Zuckerman at dinner. A soon-to-be Harvard graduate, Amanda seemed quiet and shy. She had recently spent six weeks trekking in remote Nepal, an experience that included a close look at the butchering of a goat.