Ancient Egypt experienced significant climate changes over thousands of years. Hunter-gatherer societies first inhabited the region as far back as 5000-6000 BC when the climate supported animals like elephants and giraffes. Between 3500-2800 BC, the climate dried considerably, forcing many species extinct and the development of agriculture along the Nile River. By centralizing power around 3000 BC, King Narmer was able to unite Upper and Lower Egypt, establishing a civilization that developed complex irrigation, writing, religion, and monumental architecture.