Final answer:
The Mayan civilization began collapsing over 1,100 years ago during the ninth century CE, with factors such as disease, warfare, and environmental issues contributing to its decline.
Step-by-step explanation:
The Mayan civilization entered a period of serious decline during the ninth century CE, which means the collapse began over 1,100 years ago. The Classic period of Mayan civilization is typically dated from 300 to 900 CE, with cities becoming depopulated and political structures breaking down. While the exact reason for this collapse is debated, several factors such as epidemic diseases, warfare, environmental degradation, and political turmoil are thought to have contributed. Nonetheless, the Mayan culture persisted in various forms until further disruption by the Spanish conquests, which began in the early 16th century.