213

They can't swim. Normal humans are just barely buoyant enough to float in water. We need to generate some hydrodynamic lift to get far enough out of the water to breath. The average human body has a relative density of 0.98 compared to water. Your humans would have a relative density of 1.96. That means while a normal human swimmer just needs to create a ...


160

If a civilization finds an example of advanced technology, can they learn to duplicate the technology? You have two variables: The current technological state of the civilization. Call this "A." The technological difference between the civilization and the example. Call this "B." Therefore... The earlier "A" is, the more likely the answer is "No." The ...


154

This problem has actually been considered very seriously by very serious people, in the context of warning future generations of the dangers associated with long-term repositories of nuclear waste. The Human Interference Task Force was "a team of engineers, anthropologists, nuclear physicists, behavioral scientists and others [...] convened on behalf of the ...


104

A number of common situations could give them away. If you ever paid attention to people getting in and out of your car, you notice that it shifts by noticeably different amount depending upon the weight of the person. Maybe the fact that I notice this makes me a bit of a rarity. But there are other small things. How loud a floorboard or chair creaks. How ...


99

Forts using stone, rock and earth walls as fortifications (and in some cases, still standing !) were often attacked during sieges. Such a wall has much in common with a dam. To breach such a wall you tunnel underneath. It's a well established technique. You dig a tunnel, using normal techniques to prop and seam your tunnel. Then when you've dug enough, ...


86

Laying aside the 112,000 man army (which is monstrous), I'll address Rome and the wall. Rome was entirely capable of working through almost any typical engineering problem involving such a wall. The thing about the Romans was that they were very patient. They would build a "camp" that might remain in place, working toward an objective for 20 or 30 years if ...


82

Spice Trader First they pick up lots of spices at their local Mall-Wart. Then they carry them back in time to when they were fantastically valuable. Profit! Traders come from faraway countries and don't speak Latin very well. They have exotic looks and don't even know how to tie a proper toga! And they have some weird religion that means they do odd ...


67

A more devious scheme to bring a dam down: A secret second dam above the main target dam. You simply install a second dam above the main dam (as high as possible ideally). You reduce the flow inconspicously so that the main dam manning do not see anything unusual, but slowly the reservoir of your second dam is filling. Now you wait for the perfect time ...


66

Rock and clay don't burn well, leaving you with a lot of dressed stone lying around to say there was once a city here. Fire from above implies volcanoes, as we learned from Pompeii, that's actually a great way to preserve a city so that 4000 years later we know exactly what happened, down to what specific individuals were doing when it hit, so that's out. ...


63

The Romans, or rather the Greeks, because in Roman times the vast majority of mariners were Greek, and possibly Phoenician, could have crossed the Atlantic. Technically. The classical world had extensive long distance maritime trade; ships went from Egypt to India and back routinely. They also had ships larger that the ships used by Columbus. They had lateen ...


61

The history of Ancient Rome is long, and to provide any kind of meaningful answer we need to fix a time-frame; consider that the history of the U.S.A. begins in 1776, less than two and a half centuries ago, and yet asking for how to become "part of the community" in the U.S.A. without saying in what period would be meaningless. So we must choose a period; ...


56

The Romans would mine the wall The reason that the Romans had to scale the walls at Masada is because it was built on a rockface. Mining into a rockface is hard, though it could be done, slowly. Your wall is surrounding an entire kingdom. Therefore, I conclude that some point of the wall is built on nice, soft soil. Polybius' Histories (Chapters 21.26-21....


56

In addition to the answers listed, here are some more things that these people will need to be careful about, otherwise it could put them in a situation that could result in their exposure: Speaking Their vocal cords are also twice as dense. The length, size, and tension of the folds in the vocal cords affect the pitch of ones voice. It is doubtful that ...


54

I am far from the first to think of this, but alphabetical long distance signalling, whether by Semaphore line, heliograph or shuttered lantern gives you the biggest bang for your buck as an invention to introduce from a low technological base. Given that the Greeks already had alphabetic writing many people have wondered why they or the Romans didn't think ...


52

How about a catastrophic flood? Have the city built on a large river. A landslide further up blocks the river and causes an enormous lake to form (also cutting off water supply to the city causing hardship for the inhabitants). When the dam fails...it really fails and a wall of water rushes down the valley wiping out the city and thoroughly destroying it, ...


51

Besides what everyone has already said: their steps would be generally louder. They would impact the ground with twice the energy on each step, for the same footfall used by a person of regular density. Also, they would be putting twice the pressure on the ground when standing. Their feet will sink a little bit on beach or desert sand. Their footprints will ...


50

Dredging The first thing to note when you search for dredging is that it's not Wikipedia at the top, it's an advert for a dredging contractor. This isn't something that can be ignored, it's a matter of ongoing maintenance in any managed or artificial waterway. When water enters, whether through the channel or as runoff, it carries suspended particles that ...


45

What's a "steam engine"? A steam engine is an external combustion engine which uses steam as the working fluid. So we have: Newcomen's original atmospheric engine? The Romans (or rather the Greek engineers on which the empire depended) could have copied it, most likely; using it is another question -- it's a very very inefficient engine, which was useful ...


45

If the collective mind contains memories of people, well... It contains what people remember, not the factual truth. This poses multiple problems: Conflicting memories, which may either be mutually destroyed upon merger, or lead to great levels of confusion; Poor attention. You have found the memories of the sole witness of whatever, but they didn't see the ...


43

I have much academic experience with some of this, especially the second part of your question. I'll address a few different sides of things. The most drastic way I can think of that could ostensibly be caused by some natural occurrence would be a low altitude meteoric air burst similar to the Tunguska event. Such an event would cause a lot of surface ...


41

Roman age? I can give you a stone age method: Grind it between two rocks. Silver has a mohs hardness of 2.5. Granite has a mohs hardness of 6-7. So you can use a rough granite stone to grind silver to dust. It might take a while and take some muscle, but it should work. When you are lazy, you might try to just throw your silver into a grain mill. It ...


39

Water. The misadventures on Oak Island illustrate this well. Supposedly the treasure of the Templars is there. But no-one has been able to get it. It has not been for lack of trying. https://en.wikipedia.org/wiki/Oak_Island_mystery Water in the pit: According to an account written in 1862, after the Onslow Company had excavated to 80–90 feet (24–...


38

Latin is not derived from Greek. That apart, you are probably looking for something related to Moirai They controlled the mother thread of life of every mortal from birth to death. They were independent, at the helm of necessity, directed fate, and watched that the fate assigned to every being by eternal laws might take its course without obstruction. ...


36

Where have I heard this before ? Sounds something like the plot of practically all the Indiana Jones movies, not to mention The Fifth Element and, well, lots more. I doubt this is possible. Using only Aztec or Ancient Egyptian level technology, how could the race warn the future not to mess with the evil being's prison in a way that would last an ...


35

Moved from comment to answer because I've done more research. Try the biblical account of Sodom and Gomorrah, believed to be near the coast of the Dead Sea . The cities were destroyed by means of volcanism (fire and brimstone), and 4000 years later we still don't know where they are for sure. As an argument for the effectiveness of this approach, there is ...


34

140 Watts We have the data for humans on treadmills, so the assumption is that the maximum power for a zombie is the same. They were once humans, right? You might shave off a few tens of watts due to the shuffling nature of their gait. But at least the power generation is more constant for a zombie, humans get tired too quickly. You'd be much better off ...


34

Let me see. You have no usable skills, no currency (local or otherwise), you don't speak the language, and you are not related to anybody in the area. Only one of the four of you is even remotely trained in fighting, and it will only take one stab or slash to put her out of commission. Congratulations, slaves. Welcome to your new lives. Change the tech ...


34

Simple military technology would make the biggest impact, some ideas. The longbow, along with conscript soldiers using the massed volley firing technique would outrange generally existing bows, but more importantly the ability to raise a huge force of minimally trained conscripts to provide the massed fire would be devastating to the professional soldiers/...


34

I guess there are several questions to consider when trying to answer this. Could Ancient People Have Drawn Straight Lines Tens of Kilometers in Length? The Nazca lines were up to 370 meters long, and could achieve surprisingly complex patterns. One of the hypotheses for how they did this was by drawing in a valley and having construction managers spotting ...


32

I simply do not believe that human race has a chance in your scenario. The difference in technological advancement is too huge. We are speaking about a small group of people who were able to build a space ship which was able to transport them from a distant star against people who will wait for 1000 years to be able to use gunpowder. I will try to explain ...


Only top voted, non community-wiki answers of a minimum length are eligible