(Part 1/2)

I wouldn't dare to say how likely it is but the possibility definitely exists. This is particularly true of cities from the time of the Indianised kingdoms (very roughly between 5th and 14th century), which gave us awe-inspiring and enduring structures and complexes like Angkor Wat, Borobodur, Prambanam, Trowulan and Myson. I also think there's a much better chance of finding them now than there was in the past - we’ve made some staggering discoveries in the past 10 years, sometimes by accident! The big caveat is, if we actually do find a lost city, it probably won't look as impressive as most people imagine. It may not even look like anything at all!

So why are cities from the era mentioned particularly likely to go 'missing'? The first reason is because of a lack of records. In films and TV shows like Indiana Jones, the characters often talk about legendary cities that nobody knows the locations of. In real life, that is indeed sometimes the case. For example, Mahendraparvata, which was ‘discovered’ in 2012 (more on that later), was mentioned in stone inscriptions that had been found in the Angkor area (specifically, in the Ak Yum temple near the West Baray). So we knew it existed, we just didn't know where. Or the capital of the ancient kingdom of Srivijaya. Massively rich and powerful, mentioned in Chinese records, it had to have a capital but up until recently we didn't quite know where.

But in general, records from the Indianised kingdoms are sorely lacking. Most were written on palm leaves which have long decayed or been destroyed, and there was no tradition of copying and preserving records when a kingdom fell. Ayutthaya, for example, was quite a recent and long-lived kingdom (1350 - 1767), but when the capital was conquered by the Burmese, its records were completely destroyed by the invaders. Over 400 years of history literally went up in smoke and today we have barely anything left (which touches this question asked by u/emperator_eggman). So it's certainly possible that there are lost cities in Southeast Asia that nobody is looking for because any records that might have mentioned them have long been destroyed. And, of course, without detailed records, it's very hard to figure out where a city might be even if we know of its existence.

The other problem is the lack of enduring structures. Many structures were built using wood, which doesn't last long in the area's humid climate. In Angkor, for example, bricks and stone were only used for water management projects and religious buildings. Everything else, including the royal palace, was made of wood. This could have been done for religious reasons, or it could have been because wood was readily available from the jungle, as opposed to stone which was much more difficult to get and work with.

In some cases, of course, there are clues, if you know where to look. Cities never exist in a vacuum, there is always infrastructure connecting them to other settlements or resources, and sometimes traces of that infrastructure remain.

For example, some of the rivers in Angkor meander merrily along, and then all of a sudden become unnaturally straight, a sign that a civilisation cut a canal that was so massive that it changed the river's course permanently. By and large, however, a lot of infrastructure needed some serious maintenance.

For example, we know the Khmer Empire built highways to link population centres. However, those highways were not paved roads ala those leading to Rome, they were just wide paths that were cleared of vegetation, with earth heaped on either side. When capitals moved, or rivers changed their courses, or volcanoes erupted, a lot of infrastructure got buried and swallowed by Southeast Asia's jungles.

Even graveyards are unavailable to us - the Indianised kingdoms were Hindu and/or Buddhist, and they cremated their dead. We can only look with envy at Egyptologists and their access to mummies and royal tombs!

So there may well be lots of cities in Southeast Asia we don't know about, just because we know so little. So what raises the chances of us finding them?

First of all, the political situation in the region has stabilised considerably. One of the big reasons we're so behind on studying Angkor, despite it being such an obviously important archaeological site, was because for many years the civil unrest and the Khmer Rouge regime made it impossible for studies and excavations to be carried out. The Vietnam War and its aftermath also almost completely closed the country to foreign, especially American, archeologists and historians. Today, the region is generally rather stable and much more open than before. Even so, minefields often get in the way of archaeological activities on Mainland Southeast Asia.

It’s easier nowadays to get permits to utilise new technology that can reveal exciting traces of settlements. Chief among these technologies is LiDAR, which was responsible for the discovery of Mahendraparvata, mentioned earlier. If you can get a LiDAR machine up in the air via helicopter or light plane, it can fire laser beams at the area being studied. So many are fired that some are going to get through the dense jungle canopy and down to the surface. The lasers then bounce back to the machine and are used to create a topographical map of the area. This map is accurate enough to show small bulges or indents in the earth, indicating the presence of some kind of structure underneath.

For example, in Mahendraparvata, archaeologists had unearthed various structures which seemed to be just randomly placed (if I’m not mistaken, they had to navigate a minefield to do so). However, LiDAR was able to reveal things like earthen embankments for water management and travel. Although houses in the area had long since rotted away, the mounds of earth that the houses had been built on could still be detected by LiDAR, even though they were under hundreds, maybe even over a thousand years of earth and foliage. So suddenly there was infrastructure and housing revealed that filled in the spaces between the structures that had already been uncovered, revealing the structures to be part of a city.

So there might be lost cities out there and we have the means to discover them! What might they look like? To be honest, they'd probably look pretty disappointing to the layperson.