The Indus Valley Civilization was one of the three earliest civilizations in the Old World, located along the Indus River valley in modern-day Pakistan and northwest India from 3300-1300 BCE. At its height, the civilization's cities like Harappa and Mohenjo-Daro had populations over 5 million and sophisticated urban planning with drainage and water supply systems. While its writing remains undeciphered, the civilization developed new crafts and trade. By 1800 BCE, the civilization began declining as its connections with other regions were lost and some cities were abandoned, possibly due to flooding of the Saraswati River. Around 1500 BCE, nomadic Aryan groups migrated into the region, introducing new languages and religious