"Alvaro, I'll wait for you below," shouted Alejandro, who had finished shooting. His voice brought back the dim Lima morning, when this adventure started. Jorge Chavez Airport. A murky light filtering through the windows and Alejandro's wild look as he waved desperately to me with the plane tickets. "Alvaro! Run! We're going to miss the plane." We sprinted and made it in time to our twin-propeller transport. An hour later Alejandro looked up from his book to see us dropping stuka-like towards a thin black airstrip on the edge of a gaping chasm. The colour only returned to his face when the plane had taxied to a standstill on the tarmac. We would have to get used to this sort of thing because the people in these parts prefer living in the rocky upper reaches of the mountains than in the narrow valleys.

In the overall scheme of pre-Hispanic cultures it was the Sachapuyas, after the Incas, that left behind the largest - around 500 archaeological sites - and richest architectural legacy. The historian Waldemar Espinoza thinks the Sachapuyas (whose name comes from the quechua words sacha, meaning mountain, and puya, meaning mist, a permanent feature of the area), were a confederacy of small nations united by a political alliance and common cultural traits (language, ceramics, burial customs and a distinct building style). The Sachapuyas were assimilated into the Inca empire by Tupac Inca Yupanqui in 1452. Historian Peter Lerche calculates their population at between 300,000 and 530,000, a number that declined drastically in the aftermath of the Conquest ("more than 90 per cent of the Andean population living in the province of Chachapoyas had disappeared 200 years after contact with the Europeans.").

Their language, too, was lost forever. Nevertheless, based on comparative studies of pre-Inca place names in the area, the linguist Paul Rivet concluded that the language had a Caribbean connection, especially with the Chibcha civilisation in Colombia.

However, there were things that neither time nor conquest could destroy: the myriad expressions of their art and architecture that crop up at the summit of a hill (Kuélap), in the heart of the jungle (Gran Pajatén, Vilaya) and, most astonishing of all, overlooking an abyss: the Karajía tombs, which is where we headed the morning after our arrival. What we failed to foresee, however, that the desire to follow the trail of the Sachapuyas would completely alter our plans and we would spend the next few nights roughing it, without returning to Chachapoyas until we were due to leave.

After recovering from my fright at the tombs of the dead Sachapuya rulers, I made my way down the slope to see Alejandro slouched easily astride a horse. If you hang on to its tail -he said- the climb up to Shipata will be easier. As it turned out, it was.

Back in Luya we found the district authority bus waiting to take us to Jalca Grande. We entered the Utcubamba valley, crossing colonial bridges over the lovely green river with stands of tara and molle trees crowding either bank and occasionally coming to pretty villages along the way. One of these was Tingo, where we ran into Martín and the five Americans. Sleep well? -he asked. Our yawns and stretching were answer enough.

The bus climbed up a steep, twisting side road out of the valley. The first things we saw of Jalca Grande were its high, occasionally conical roofs. The village was built on pre-Hispanic ruins. One corner of the Plaza de Armas is occupied by a stone church built in the 16th century, while on the opposite corner stands a museum that contains among its relics the vestments brought by the original priests, some of which are four hundred years old and embroidered with gold and silver thread. The museum also boasts Sachapuya ceramics and stone utensils among its exhibits.

That night we slept under the stars and were up at dawn roaming the ancient village. From the lower end of the village we could clearly make out on top of the mountain on the other side of the valley the imposing ramparts of the Kuélap fortress. It was time to get a closer look. We went back to the village of Tingo, where the signs of the mudslide that all but destroyed it in 1993 are still evident. If you're fit you can reach Kuélap after a 4 or 5-hour climb. Our problem was that we had to fly back to Lima the next day, so we drove, taking a route that passes through the villages of Longuita and María and deposited us at the foot of Kuélap, at an altitude of 3,000 meters.

This magnificent megalithic construction was officially discovered in 1843 by judge Juan Crisóstomo Nieto. His description of the ruins - the dimensions he recorded meant its volume was three times that of the Great Pyramid of Cheops - attracted the attention of several scientists, including Antonio Raimondi (1860), the Swiss geologist Arthur Wertheman (1870- 75), the French explorer Charles Wiener (1881) and the Swiss anthropologist Adolph Bandelier (1893). While Alejandro went to work, I stood in front of a colossal wall 584 meters long by 20 meters high that I first visited years previously. Then I noticed the same ungainly fortress caretaker I had seen back then. His name is José Portocarrero and he has been protecting Kuélap from latter-day invaders for the past eighteen years.