''Just follow the Inca road!'' and with that, Jaime, my guide, was gone - down a long, dizzyingly steep slope of crumbling red scree, down along the edge of the huge glacier to our left, whose surface has been smoothed by severe wind and etched by debris to the look of burnished silver. He was quickly a small black figure lost under the towering white brilliance of Salcantay, the mountain peak that dominates everything within miles. I was left alone on the razor edge that is the summit of the Incachilaska Pass, 16,000 feet up in the Peruvian Andes.
Across high, bare, undulating olive land, the imprint of the road curved below me - a thin thread, still visible after three centuries. Along it, far in the distance, walked tiny specks, strung out over and between the great rounded wrinkles, the other seven members of a trek organized by Mountain Travel.
The builders of the road called it Capac Nan, the beautiful highway. It was the technical means by which they administered an empire that at its height reached 3,000 miles along the Pacific coast of South America. It was the royal road of the Inca - supreme ruler - whose title the conquering Spaniards, reaching Peru just at the apogee of imperial expansion, misapplied to the whole civilization. So magnificent were the roads - over 5,000 miles of them with almost 1,000 bridges - that Hernando Pizarro himself was awed: ''The royal road over the mountains is a thing worthy of being seen, because the ground is so rugged. Such beautiful roads could not, in truth, be found anywhere in Christendom.''
The Andes are precipitous ridges of rock, the second highest range in the world. On one side is the arid coastal desert, and on the other the almost impenetrable jungle of the Amazon basin. High fertile valleys among the mountain peaks provided a habitat conducive to the development of civilization. A road system was essential to the empire in such terrain, but the obstacles to its construction were so great that it stands as an engineering feat of extraordinary brilliance, far greater than that of Rome - unbelievable in scope and precision, were one not actually walking on the stones.
The feat that it was was indelibly clear to me as I stood under Salcantay. It had been imprinted deep in the fiber of mind and muscle with every step to the top of the long and extremely steep pass. We had begun the trek two days ago in Cuzco, a city of golden Spanish provincial architecture underlaid with the massive walls of original Inca buildings - a city with the austerity of both the Inca and El Escorial. Cuzco - capital of the Inca empire, and for the Inca civilization, literally considered to be the ''navel of the world.''
Out from the city, we were immediately immersed in the intense quality of Peruvian light. The landscape itself is arguably the most spectacular on earth. The Andes are like elegant, soaring white wings. They are not massive in aspect like the Himalayas nor weathered like the Alps, but rather are thin and tapered, jagged knife edges. But the dark, brooding light that falls around the mountains imparts a power to the landscape that is much more than simply beautiful. Gray often hangs low and ominous over the peaks while sun streaks the high plains brilliant green. Shadows color great swaths of the brown hills dark lavender-blue.
We climbed initially through steep, arid ridges far above a wild, churning stream, past stands of twisted trees baroque with lichens and bromeliads. It is a landscape with red butterflies stationary in the trail, and bright blue buntings fluttering about unafraid among voluptuous blossoms.
Walking always toward the white of Salcantay, we came to a great highland meadow of light brown grass. And there we camped under the mountain in the thin, silent air of a long dusk.
The next day we scaled two more high passes, walking on this tiny track through a world unknown below this altitude: empty, desolate, echoing country, bare and chillingly remote. It is without snow and ice, a vast expanse of unrelieved rock falling away into a far distance.
Names for the land in Peru are descriptive references to what grows in each zone of altitude. There is the junga, or jungle, the quechua, where the corn grows, and the puna, where no corn grows. Altitude is so vital in Peru, that the name of the level that produces life-sustaining corn is also the name of the Inca language, Quechua.
We camped, poised to descend through the inhabited strata of Peru's vertical agriculture. The next day, we would pass men harvesting potatoes from small fields blocked out from the enormous scale by what seemed doll-like stone walls. And much farther down we would pass through a whole village taking in corn. But on our second night, we stayed in the high puna.
To say that we ''camped'' is accurate in that we stayed in tents on the ground in sleeping bags. But trekking with Mountain Travel is trekking with style. Our dining room table came with us on mule back - and the dining room with it (in the form of a large tent). We sat down to tea at the end of our first day with strawberry preserves and English biscuits. At the second camp we dipped into freshly made popcorn. I will long remember a superb lunch prepared in the middle of one of our longest days - a day of climbing steeply up through wet forest, down over irregular jumbled rocks, and immediately up again, up a mountain side so steep that we crept along a zigzig of switchbacks. Juan, our chef, managed elegant plates of papas a la Huancaina in the spectacular setting of a round pre-Inca ruin.
Mountain Travel puts every effort into seeing that all members complete the trip - not a trivial concern with 16,000-foot passes in rapid succession. It is a rigorous trek. There is a wonderful exhilaration in the physical exertion. But the leaders help that exhilaration along by bolstering flagging confidence. ''We all make it!'' was the smiling response to a few hesitant verbalized self-doubts at the end of the first long day. And the leaders ensure that we do make it by assisting in the ruthless paring down of daypack loads and in adjustments to equipment.
Below Salcantay, we turned onto what was originally a minor spur of the Inca Road. It was for centuries unknown or ignored as an unimportant dead end. It is now by far the most heavily traveled portion and is known as ''the Inca Trail.'' It leads to the sacred late-Inca city of Machu Picchu.
Because this secondary road did not receive the heavy traffic the rest of the system carried well into the 19th century, it is well-preserved. Precise curbs remain; stairways with great stone slabs as risers lead up to lookout posts; steps are cut into bedrock through natural tunnels. There is also increasing evidence of what Inca civilization was like before the Spanish conquest: the garrisons of Sayacmarca, Phuyupatamarca, and Huinay Huayna. Each is different in character and orientation to its site, but the salient characteristics of Inca workmanship stand out: long concentric terraces down the steep mountainsides, trapezoidal windows looking out to triangles of sharp peaks; and, above all, the huge stones superbly and precisely joined without mortar.
At the turn onto ''the Inca Trail,'' we passed to the wet side of the mountains and entered a lush cloud forest, dripping orchids and tendrils of vines - a cool, still-silent world of tree ferns over and beside the rock. The last bit of trail edges along a precipice. Several times I put my walking stick down beside my foot into what looked like foliage but was, in fact, empty space. The precarious way the road hugs the mountain is disguised by luxuriance. For a long stretch, the ground is coated with white blossoms fallen from giant trees that tower in the canopy.
I came to a high fortress-gateway in late afternoon. Machu Picchu lay below just as I had seen it in innumerable photographs - a collection of almost intact stone ruins on a small saddle of ground in the midst of sheer green mountains.
The site can, of course, be enjoyed on many levels. You can give yourself over totally to the visual and walk through Machu Picchu as through the Museum of Modern Art. Superlatives hang limp and ineffectual beside the magnificence of Inca art and masonry. An enormous stone in the ''Ceremonial Room'' has 32 angles worked on all six sides. The Intihuatana, the most sacred of Inca shrines, at the highest point in the city, is bedrock carved into an abstraction, every side of which is different and subtle. Examples of the daring and accuracy of Inca stonework are everywhere: the exquisite cascade of fountains, the great carved stone by the ''Watchman's Hut.''
Machu Picchu is a great, terribly intricate and beautiful Rubik's Cube.
Rock and water are clearly paramount. The Incas seem to have venerated both, and often bedrock was left untouched next to detailed carving. The planning of the trek allowed us to experience in an immediate way the parallel of art and nature.
Peru is magnificent. But just when you settle in to love the land and reach out to embrace its beauty, it reminds you that it is harsh and unforgiving.
The Incas built the Royal Road in harmony with the land. It is a great irony that the very excellence of this achievement was the avenue to their destruction. It was by following the beautiful road that the small band of Spanish conquistadores was able to obliterate the Inca.
The Mountain Travel trip described is a three-week trek called ''Peruvian Highlands.'' It is quite strenuous, and to undertake it one must be in excellent physical condition. Other Mountain Travel treks in Peru are less rigorous, and some are even more so, requiring mountaineering skills. The Peruvian Highlands trek is $1,850 to $2,150, excluding air fare, depending on the number of participants. Hotel accommodation is included in the trip price; but if you spend additional time in Cuzco, I recommend the Libertador, an old Spanish mansion built on Inca walls. The Gran Hotel Bolivar in Lima is one of the great hotels of the world. For places to view Inca artistry in Lima and Cuzco, see page B11. Aeroperu flies to Lima and then to Cuzco from Miami.
There is political unrest in Peru near Ayacucho; Cuzco and the vicinity of the trek are far removed from the problem areas.