Though the Romans were militarily superior, they were at a quick disadvantage in terrain. This allowed the Aztecs to wage a guerrilla war against the Romans, until domestic pressure forced the Romans to withdraw. However, Roman technology and strategies were absorbed by the Aztecs, allowing them to advance their military further. This lead Emperor Huitzilihuitl to rename the Aztec Empire, the Aztec Hegemony.
The Aztecs and the Romans had already been in contact with each other before the war, with a Roman consulate present in their capital of Tenochitlan. Tensions between the two were initially relatively minor, until the Roman ambassadors observed human sacrifice atop. They sent a message to Europe, where the Bishop of Rome called for complete conversion of the Aztecs. The Roman Senate refused these requests, not interested in an overseas conflict with another Empire.
The Roman delegates later were invited to a festival celebrating the god, Tezcatlipoca. As a courtesy the offer was accepted, but when a man was about to be sacrificed, one of the delegates interfered, a crime punishable by death. The delegate was summarily executed as a sacrifice to the God of the Smoking Mirror.
Word of this soon reached the Roman homeland, which spurred the Senate to order General Aemilianus Aeitus, and a full legion to Azteca, to conquer the Aztecs. The legion landed in Cuba, before advancing to the Mexican land.
Course of the War
While the Romans were better armed, and better organized, they had little to no experience operating in the jungles of Central America, and were at a quick disadvantage in terrain. Taking advantage of this, the Aztecs attempted to launch a full campaign against the Romans, but the Roman use of gunpowder put their armies at a disadvantage.
Aeitus briefly considered simply burning the forest down, but was dissuaded by his officers, reasoning that it would take a long time, which the Romans did not have the capacity for. Deciding to change tactics, Huitzilihuitl instead decided to use the terrain as he could. Instead of trying to battle the Romans in an outright war, he instead had his troops harass, and impede the Roman advance, launching small scale raids and skirmishes against legion.
Sands of Blood
The guerrilla war soon took its toll on the Romans. The Aztecs would lead them into areas with natural hazards, and release venomous snakes into their camps. Mutiny began to spurn throughout the Roman armies, and some even deserted, or defected to the Aztecs. A final defeat was inflicted upon the Romans, when their remaining forces were ambushed on the beach. Running low on precious gunpowder, the Romans were forced to fight without it, which swung the battle in the favor of the Aztecs. In what became known in Rome as "De Sanguine Harenae" (lat. "sands of blood), over a thousand Roman lives were lost, including General Aeitus. The remaining Roman soldiers were forced to retreat back to Cuba.
When word of the slaughter on the coast reached Rome Primera, the Roman public began calling for the return of the Legion, and for the end of the efforts in Azteca. Despite continued protests by the Bishops (who were still demanding that the Aztecs be forcibly converted), the Senate voted in favor of ending the war, and staying out of the Aztec's way for the foreseeable future.
The Aztecs opted to not attempt to pursue or get involved with the Romans either, choosing to stay away from the islands under their control.
The impact the Romans had on the Aztecs was maintained. Roman weapons, armor, and strategies were absorbed into Aztec military, including the use of gunpowder. With these new weapons, as well as horses which were acquired from the Romans, Aztecs then continued their war of conquest, expanding rapidly both North and South. Huitzilihuitl proclaimed a new era for the Aztecs, and declared the establishment of the Aztec Hegemony.
An actual treaty of peace was not formally signed until over a hundred years later, where the Proconsul authorized an ambassador to return to Azteca. A formal treaty was signed, and the Romans were allowed an embassy once again, though the slight advantage they had, was now completely gone.