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.
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."
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.
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.
Dr. Khurram Qadir directs Pakistan's National Institute of Historical and Cultural Research. He says references to Egypt and the pharaohs in religious texts have made ancient Egypt more familiar.
"The Pharaonic past is neither Jewish, nor Christian, nor Muslim, but it is a common tradition to all three of us. And because the Egyptian remains have that lure, it's so much more powerful," Qadir says.
He says most Pakistanis are not interested in the Indus civilization.
"Being pre-Islamic, it is not an area which is of, it would not take prime time out of our viewership," Qadir says.
Experts say archaeologists have only excavated about 10 percent of the two ancient Indus centers.
"We have a great shortage of funds in our archaeology departments. We are barely able to do conservation work or maintain what work has already been done," says Qadir.
Gul says the ancient city of Moenjodaro receives UNESCO funding because it is a World Heritage site. But its sister city Harappa, which is not yet on the list, is in need of help UNESCO cannot afford.
And with money unavailable to prevent the saline topsoil from damaging new excavations, Gul says the best option right now is not to dig.
"Let them be, don't touch them, because they're better that way," says Gul. "At least they are preserved underwater."
For now, many keys to the ancient Indus remain underground, waiting to be discovered.