As many planets with civilisations as there are, there are at least twice as many without. These planets don't usually get the history they deserve, simply because there was no one around to document it.
Some time ago, during the hey day of colonisation, planets started to be discovered that had structures on the surface which could not be explained by the existing species on them. When the research came back and the data was summarised, the only answer that could explain everything was that these things had been put there by visitors before us.
That idea was heretical to a lot of people. As far as they were concerned, we were the first and only ones to ever make it out into the deep black.
More philosophically, the idea that someone, or someones, had been around long enough to evolve to the point where they were able to travel through space and visit planets seemingly on a whim, leave immense structures which, in some cases, took some months to enter thanks to a complicated series of locks, and then disappear without a trace caused them to speak at length about how space travel was detrimental to a species and used that rhetoric to argue against our attempts to do so.
Despite the fears of these people, space travel, and colonisation, didn't end in disaster and when it was all said and done, we had discovered nearly a dozen of these structures, each with their own methods of entry which prevented the native creatures – none of which had evolved to a point of real intelligence – from entering.
Within each of these structures, we found very large written records. For the time being, we are unable to translate much of it, but what we do know seems to indicate that it is a historical record of the planet and the species that were found on it. While some of these planets do not have a permanent colony on them, we have left satellites in orbit, watching and waiting to see if these record keepers return.
The crystal clear water lapped up on the shore while dark, angry clouds sat low on the horizon, waiting for the sea breeze to abate so they could unleash their heavy cargo over the coast.
The small creatures brayed to each other calmly as they made their way down to the water. They knew night was close and the predators would be waking soon. This would be their last visit to the water for the day and when they had drunk their fill, they would be heading back to the nearby hills where their nests were.
Seabirds flapped around their heads, cawing loudly, hoping there was some leftover meat for them to scavenge, despite these small creatures being herbivores.
They hunched down over their cloven hooves and lapped at the water quickly and efficiently. A crack of thunder overhead startled them and they cut short their evening drink and took off back towards the hills.
The sea breeze shifted suddenly and the smell of rain drifted over the coastline. The birds which had roosted along the high tide mark, once the other creatures had started back to the hills, ruffled their feathers and a few of them cooed lightly. The drizzle started a few minutes later and would have grown into one of the areas regular intense rainstorms had it not been for the visitor who had been sitting over this whole scene for as long as any of these creatures could remember, unmoving, unspeaking and completely uninteresting to the few creatures which made this sandbar their home.
The visitor had two legs, which were crossed over each other and two arms which rested on the upper part of the legs. Its skin was a two tone grey, with darker markings around the muscle lines.
A light blue crystalline object throbbed irregularly with light in its chest. It didnt seem to be related to anything the visitor was doing, nor did it coincide with anything that was happening on the ground below it.
The visitor was almost 15 meters tall and hovered anywhere between 100 and 300 meters above the ground. Its head carved a line through the fog that had crept along the shore in advance of the storm behind it.
In the moment following the crack of thunder and the animals running back from the water, a brilliant blue-purple light had flashed from an opening in its head and everything froze. In this captured moment, the visitor turned its massive upside down tear drop face head to observe everything. This made no noise, and caused no movement of anything below it.
Back in the hills, where the startled herbivores were making their way for the night, several lithe, black shapes could be seen just behind the treeline. Nocturnal predators, up early for their hunt. These creatures would intercept the others within minutes, and their visit to the water would prove to have been a mistake. The visitor made no effort to interfere with this, or any other, chain of events.
What the visitor did do was shape some of the sand into sandstone blocks, and in turn use these blocks to create an immense labyrinth on the beach. Each wall of this structure was covered with runes and markings which depicted anything from the star that fed this planet, some 400,000,000 kilometers away, to the tiny little bugs that lived in the sand the building was being made from. The labyrinth started many miles back, where the beach started, and the visitor showed no signs of stopping it any time soon. This one, along with others that had been made on this continent were a specialty of this particular visitor. All over the planet, there were others like it doing the same. Watching, recording and leaving everything.
They knew they would never reap the rewards of this gambit, and in the long term, it wasn't even likely that anyone would find these repositories, but they kept at it, moving from each planet with life to the next, recording and saving.
There came a day when our species came into direct contact with these visitors. The single most historic day ever. And the worst.