The Mayans came first, predating the Aztecs by several centuries. The Mayan civilization began to flourish around 2000 BCE and reached its peak during the Classic period (250-900 CE). They were known for their advanced writing system, mathematics, and astronomical knowledge.
In contrast, the Aztec civilization emerged much later, around the 14th century CE. The Aztecs built their empire in central Mexico and are famous for their capital city, Tenochtitlán, which is now modern-day Mexico City.
While both civilizations made significant contributions to Mesoamerican culture, the Mayans were already in decline by the time the Aztecs rose to power. The Spanish conquest in the 16th century ultimately led to the downfall of both civilizations.