The Indus civilization encompassed more than 680,000 square kilometers, from western India to northern Afghanistan, double the area of ancient Egypt and Mesopotamia combined. Although the civilization had some of the earliest writing, several factors have kept clues about the ancient Indus people buried underground and under the Indus River.
The ancient cities of Harappa and Moenjodaro, hours south of Islamabad by land, were the two largest centers of the Indus civilization.
Unkown factors
Indus artifacts like these shed light on daily life here more than 4000 years ago. But much is still unknown about the Indus people's communication, religion and political organization.
Fahrat Gul, head of UNESCO's head of culture for Pakistan, says the area is remote and that has hindered work there.
"It's rather inaccessible. Even we don't have daily flights to Moenjodaro," she notes. "You have to come either via Karrachi or via Sakkur. And then the airport in itself is not a proper airport, a very very small one."
Earliest writing
Indus artifacts contain some of the earliest writing in the world. This fragment of script is at least 4,400 years old.
But there are so few writing samples that the ancient language cannot be deciphered.
Archaeologists say the most striking thing about the sites is the Indus civilization's city planning. They had wells and drainage systems. They had streets made at right angles. Even the bricks used in Harappa were the same size and weight as those used hundreds of kilometers away in Moenjodaro.
Security problems
The security situation in Pakistan has also hindered archeologists and preservationists at the sites.
"It has restricted our mobility," says Gul. "Especially our monitoring missions have been restricted. We cannot go to these places to monitor the progress of our projects, which does have an effect."
While millions of foreign tourists travel to Egypt every year for its museums and ancient monuments, at most a thousand foreign visitors come to Harappa every year.