1202
Fibonacci publishes Liber Abaci
A Pisan merchant's son who had learned arithmetic in North Africa laid out Hindu-Arabic numerals for Latin Europe. Among his worked examples was an idle puzzle about breeding rabbits whose answer unfolded a sequence that would haunt mathematics for the next eight hundred years. The book's practical chapters on currency conversion and profit calculation transformed Italian commercial bookkeeping overnight.
Anasazi begin cliff dwellings at Mesa Verde
High in the sandstone alcoves of southwestern Colorado, Ancestral Puebloan builders laid the first stones of what would become Cliff Palace. Generations later their descendants would abandon the cliff houses as drought and violence drove them south into the Rio Grande valley. The ruins, tucked beneath overhanging rock in canyon walls, would remain hidden from outsiders for another six centuries.
Crusaders sack Christian Zara for Venice
Unable to pay their passage, the Fourth Crusade's knights agreed to capture the Adriatic port of Zara on Venice's behalf. Pope Innocent III excommunicated the entire host for drawing swords against fellow Catholics, then quietly rescinded the sentence against the French. The precedent of holy warriors serving commercial interests would repeat itself, with greater consequences, at Constantinople the following year.
Champagne fairs at their medieval peak
In the rolling country east of Paris, merchants from Flanders, Lombardy, and the Rhine met six times a year to trade wool, spices, and silver under the counts of Champagne's protection. The fairs functioned as medieval Europe's clearinghouse, their letters of exchange teaching bankers their trade. Provins, Troyes, Bar-sur-Aube, and Lagny each hosted its season, creating a continuous commercial calendar.