Just over a week ago, I took a short trip to the crumbly, beautiful ruins of the Angkor temples in Siem Reap, Cambodia. I had visited them before, over a decade ago, but only for several hours as a sort of transit point. Our journey through the temples had been hasty, unguided, and largely uneducational.

This time, my husband and I were prepared to spend two days on the temple complex, jostling with thousands of other tourists and armed with Khmer expert Claude Jacques' guide to the more prominent temples of Angkor.

There had been a heavy storm the night before and the long, broad causeway across the moat to Angkor Wat was studded with puddles; the overall effect was that the path towards its silhouetted towers seemed to gleam and glitter in the early morning light.

There has always been something quite otherworldly about the centuries-old ruins I have visited over the years. The temples of Bagan in Myanmar, with more than 2,000 pagodas scattered across wide, dusty plains, their stupas stretching towards the sky; the impossibly large stone edifices of Machu Picchu, solid and square, its reason for existence still a source of debate.

We scaled several steep temples in Angkor Wat and Angkor Thom on the first day, the two more well-known complexes adorned with bas reliefs in astonishing detail. The South Gallery of Angkor Wat boasts a 94m-long military procession depicting 12th-century ruler King Suryavarman II in several poses - including one astride an elephant beneath 15 parasols. As befitting someone of his stature, his figures are larger, by far, than his hundreds of foot soldiers and dozens of princesses on palanquins.

Like the Egyptian pharaohs with their pyramids and glyphs, rulers for centuries have sought to create architectural marvels that would sustain their legacies across generations, even temples created for religious purposes, each trying to outdo their predecessor in terms of devotion. But the expression on King Suryavarman II's face has eroded over the course of several hundred years. You can barely make out his almond-shaped eyes, or the curve of his mouth.

One of the largest temples we visited was Preah Khan, created during the reign of Jayavarman VII in the late 12th century. He was responsible for many of Angkor's most recognisable structures, including the eerily overgrown Ta Prohm, now often referred to as "the Tomb Raider temple" because it was used as a backdrop to the action flick starring Angelina Jolie.

Each of the four entrances to Preah Khan is guarded by enormous statues. But most of these moss-grown guardsmen are missing limbs or swords, and none of them have retained their heads. They stand there, left hand over their chests, pledging allegiance to no one in particular, and mostly ignored by tourists more interested in taking pictures with a nearby strangler fig whose roots have swallowed up half a gallery.

Half-remembered phrases from Percy Bysshe Shelley's poem Ozymandias (1818) filtered into my mind as I paused to look up at these headless soldiers. A traveller wandering across a desert comes across a fearsome statue of a king - except that his snarling face lies in the dust. The words carved onto the pedestal are rich in hubris:

'My name is Ozymandias, king of kings:

Look on my works, ye Mighty, and despair!'

What a king, you might think, but then you read on:

Nothing beside remains. Round the decay

Of that colossal wreck, boundless and bare

The lone and level sands stretch far away.

In the case of Angkor, it is perhaps the thick tropical jungle that stretches far away. King Suryavarman II may have carved himself into stone, expecting his likeness to live forever. But today, he is mostly a backdrop for trigger-happy tourists with selfie sticks - perhaps not quite the legacy he was hoping for.

What will our own ruins look like centuries into the future, when we are long gone?

During the trip, I happened to be reading Neal Stephenson's Seveneves (2015), a post-apocalyptic slab of a novel that imagines the destruction of the earth and the survival of humanity five millennia later. In his methodical re-envisioning of a future history, even the basic genetic structure of the human being has altered over the course of five thousand years of evolution. But of earth, "nothing beside remains".

When Shelley wrote, "Look on my works, ye Mighty, and despair!", I think this despair was not merely one of fear or awe at a king's sprawling empire. It is also a despair of encroaching time, that no matter a ruler's attempts to control his legacy, it will be interpreted and manipulated in any way the future wishes.

The final temple we visited was in the East Baray, a long swathe of land that was formerly a reservoir but has since dried up. We climbed to the top of the East Mebon temple, an impressive three-tiered structure built in glowing red laterite and with elephant statues at each of its corners. Some tourists had clambered roughly on top of one of the elephants and were taking candid photos.

Beneath us, scrubby trees stretched across the landscape, eventually giving way to green rice fields. The sun was sinking lower on the horizon and darker rain clouds were gathering. The tops of several towers were visible from our vantage point, each bearing faces of deities smiling beatifically at the surrounding forest.

I ran my fingers over the coarse edge of a sandstone block. Kings often died before their temples were completed, leaving their successors to finish the task. A king might have stood here a thousand years ago, watching the weather change, looking down at his kingdom and wondering how long his reign might last.

Then we climbed back down, got into our rented car and drove back to our hotel for cocktails as the rain came down.

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