Harappan civilization, also known as the Indus Valley civilization, was one of the world's earliest urban civilizations, flourishing around 2500 BCE in the region that is now modern-day Pakistan and western India. The civilization left behind a rich archaeological record that provides valuable insights into their way of life, trade networks, and cultural practices. While there are various sources of evidence to ascertain the date of the Harappan civilization, the best evidence is the presence of Harappan seals in Mesopotamia.

The Harappan seals were small, square or rectangular objects made of terracotta or steatite (a soft stone). They were intricately carved with various motifs, including animals, humans, and script-like symbols. These seals were used for a variety of purposes, including marking ownership, indicating authority, and sealing containers or packages.

The presence of Harappan seals in Mesopotamia, which is located in modern-day Iraq, provides a strong indication of the time period in which the Harappan civilization existed. Mesopotamia was home to several ancient civilizations, such as the Sumerians and Akkadians, who had established trade networks with the Harappan civilization. The presence of Harappan seals in Mesopotamia suggests that there was active trade and cultural exchange between the two regions.

The Mesopotamian seals found in Harappa further confirm the existence of these trade networks. These seals, which were made by the Mesopotamians, were found in Harappa and other Harappan sites. This indicates that goods and ideas were flowing between the two regions, further supporting the idea of an interconnected and thriving civilization.

The presence of Harappan seals in Mesopotamia and Mesopotamian seals in Harappa provides a cross-cultural link and helps archaeologists establish a chronological framework for the Harappan civilization. Studying the context in which these seals were found, such as their association with other artifacts or structures, can provide additional clues about the time period in which they were used.

In conclusion, the presence of Harappan seals in Mesopotamia and Mesopotamian seals in Harappa is the best evidence to ascertain the date of the Harappan civilization. These seals provide valuable insights into the trade networks and cultural exchanges of the time, helping archaeologists establish a chronological framework for this ancient civilization.