In the high, windswept plains of what is now Bolivia, a single mountain reshaped the world. The Cerro Rico, or “Rich Hill”, of Potosí was a near-solid mass of silver, a discovery that flooded the Spanish Empire with unimaginable wealth from the 16th century onward. This silver funded European wars, fueled a global trade network, and created an opulent colonial society. But that mountain of silver was just that—a mountain. For its wealth to become power, it had to be moved. And in the perpendicular world of the Andes, where wheeled carts were useless, the entire imperial enterprise rested on the sturdy back of the humble mule and its master: the arriero, or muleteer.

The Four-Legged Engine of an Empire

Before the Spanish arrived, the Inca had masterfully managed logistics with vast llama caravans. Llamas were perfectly adapted to the altitude, but they had their limits. They could carry relatively light loads (around 30 kg) and could be stubborn, refusing to move if overworked. They were sprinters, not marathon runners, in the world of logistics.

The Spanish economic model, built on extraction on an industrial scale, demanded something more. The answer was the mule, a sterile hybrid of a male donkey and a female horse. Mules inherited the best traits of both parents: the strength and size of a horse, combined with the endurance, intelligence, and incredible sure-footedness of a donkey. A single mule could carry over 100 kilograms of cargo, day after day, across the most punishing terrain on earth. They were tough, able to subsist on sparse high-altitude vegetation, and resilient in the face of the Andes’ extreme climate.

The demand for these animals exploded, creating a massive mule-breeding industry in the fertile plains of what is now Argentina and Chile. Tens of thousands of mules were driven north each year in great herds to be sold at markets that supplied the mining zones. They were the living, breathing engines that powered the colonial economy.

A Life on the Trail: The World of the Arriero

A mule train was nothing without its arriero. These muleteers were the masters of the trail, the men who knew every pass, every treacherous river crossing, and every weather pattern. They were a diverse group, often drawn from the margins of colonial society. Many were mestizos (of mixed Spanish and Indigenous heritage), but they also included Indigenous men seeking to escape the brutal forced labor of the mines (the mita), as well as free and enslaved people of African descent.

For them, the life of an arriero was one of grueling hardship, but also one of relative freedom and opportunity. Unlike a miner or a field laborer, the muleteer was his own boss on the open road. His status was defined not by his race, but by his skill, his reputation for reliability, and the quality of his animals.

Life began before dawn, rounding up and loading the mules—a complex art of balancing weight to prevent injury to the animal. The days were spent walking, covering 15 to 25 kilometers through dizzying altitudes that would induce crippling altitude sickness, or soroche, in the unacclimated. Nights were spent in rudimentary inns known as tambos, or simply out in the open, with the muleteers sleeping among their precious cargo and animals, ever-vigilant against bandits and predators.

The Silver Veins of the Andes

The mule trains were the circulatory system of the Viceroyalty of Peru, connecting the mines to the cities and the ports. The most critical routes were a two-way street of supply and extraction.

• The Mercury Route: Silver could not be efficiently extracted from its ore without mercury. The primary source was the “mine of death” at Huancavelica, in central Peru. Mule trains would haul the toxic liquid metal in specially sealed leather pouches for hundreds of kilometers over the mountains to Potosí. Without this mercury, silver production would have ground to a halt.
• The Silver Route: Once mined and refined, the silver was cast into bars stamped with the royal seal. The arrieros would then load their mules for the perilous journey out. A primary route led west from Potosí, down the Andes and across the bone-dry Atacama Desert to the port of Arica. From there, it was loaded onto ships and sent north to Lima’s port, Callao, before joining the Spanish treasure fleet bound for Panama and, ultimately, Seville.

But these weren’t just silver and mercury highways. The arrieros carried everything the colonial world needed. They hauled wine from coastal valleys, coca leaves (chewed by miners to endure the horrific conditions), textiles from Quito, tools, grain, and even luxury goods for the wealthy elite in the mining cities. They were the Amazon delivery drivers of their day, but with more mountains and fewer paved roads.

The Social and Cultural Hub

The arriero was far more than just a delivery driver. On their long journeys, they were the primary conduits of information, news, and culture, connecting dozens of isolated mountain villages and towns. They carried letters, government decrees, and—most importantly—gossip. The arrival of a mule train was a major event in a remote settlement, bringing not just goods but contact with the outside world.

Economically, they were entrepreneurs. A successful arriero might own his own train of mules, hiring others to help him. They often bought goods in one town to sell for a profit in another, engaging in small-scale trade and acting as mobile merchants. Their rugged independence and knowledge of the land gave them a unique and respected place in the social hierarchy. They were seen as tough, worldly, and reliable figures, embodying a fusion of Spanish and Indigenous knowledge necessary to survive and thrive in the Andes.

For centuries, the rhythmic sound of mule bells was the sound of commerce and connection in the Andes. While the kings in Spain counted their silver, and the viceroys in Lima administered their territories, it was the anonymous muleteer, navigating a treacherous pass at 4,000 meters with his loyal animals, who truly held the empire together. They were the unsung, essential gear in the great machine of the Spanish silver economy, and a testament to the human resilience required to tame one of the world’s most formidable landscapes.