1520
La Noche Triste (The Night of Sorrows)
The setting
Tenochtitlan causeways, Lake Texcoco
Narrow causeways across a lake with gaps/canals; night
Reveal the outcome
Spanish attempting to flee the city at night were caught on the causeways and routed; many drowned or were killed, weighed down by looted gold
How the atlas explains it
The Aztecs caught the Spanish strung out on narrow causeways with broken bridges, negating cavalry and firearms and exploiting darkness and water. Encirclement on confined terrain and the collapse of Spanish cohesion turned the retreat into a slaughter.
What followed
The worst Spanish defeat of the campaign; nearly ended the expedition, but Cortes regrouped with Tlaxcalan support.