Mules and the arriería — the freight system of Spanish South America, costed by a 1773 road book

Everything moving inland in Spanish South America moved on mules, and a book printed in 1773 describes the industry from inside: the trick that made a mare raise a donkey foal, the price of a mule at each stage out of the pampas, the six-hundred-head droves assembled at Salta, and the finding that a well-fed coastal mule worked twenty years where a sierra mule worked five.