Dear @Amir, Viminacium is in my vicinity. I do find Roman Aqueduct as one of the greatest ancient engineering inventions of all time. I have attached one photo, see many of them by link given bellow.

http://viminacium.org.rs/en/arheoloski-park/akvedukti/

Individual dimension: The engineers' inventions you use (almost) daily?

Population dimension: ???

Dear Marcel,

Generally speaking. For example skills and techniques for: measuring mass, measuring distance, measuring time, motors, distribution of water, lift and transports ....

Ten amazing inventions from ancient times

http://www.ancient-origins.net/ancient-technology/ten-amazing-inventions-ancient-times-001539

The Romans called the mixture of lime and pozzolana opus caementicium. This conglomerate cannot be defined as either cement in the modern sense nor as concrete.  

The measuring of distance  represent the first step in the development of science and technology.  Thaletes, Pythagoras, Archimedes were deeply interested in the study of geometry. In building temples and towns, accurate measuring of distances is essential. 

Dear Amir!

This is an absolutely thrilling question to try and answer. There probably is no universal answer...

Thank you.

As I first read , I imediatly thought of of the most obvious answer to give , as I was taught that the WHEEL was probably the best human invention ever made. 

Then I thought of one of the most interesting books that I am slowly reading - I usually read 5 or 6 simultaneously- : «Neil McGregor (2010) A History of the World in 100 Objects. Penguin.». Quite, quite interesting. (Even the author found serious difficulty in selecting the 100 best objects...

From my very own personal and anthropological perspective, I should answer that the best juman invention of all times was the intelligence to perceive the ability of his own hands, to be used as instruments...

ARISTOTLE reffered to the Human Hand as «The Instrument of the Instruments»

Then again, all depends on the scale of analysis.

Example

Some people might ask: Is the wheel the greatest invention in the framework of climate change?

It's all about costs and benefits which may change in time?

Dear Amir

I would say it is the 'Arch' (for roads, bridges, pipelines, etc.,), which would have come before the wheel. Even the Chieftain's house would have had one, I am sure.

Keep well

Narayanan

What about wings on the sea -The sails ?

Dear Maria, I appreciate this. Human Hand as «The Instrument of the Instruments» is excellent proposal.

Dear Amir,

Nice question.

After reading your question, I thought about astronomy.  Thousands of years before, my ancestors predicted clearly about solar system and position of planets, and their predictions.  During their time, even paper is not invented. They have used palm leaves and nails for writing.  All their concepts were verified/proved only few hundred years only.

As mentioned in the previous posts, speech or wheel etc.... were necessary to make their everyday life comfortable. But something sparked them to think/research about planet and solar system with only mind power. We took thousands of years to advance our  scientific knowledge  to verify what they achieved without knowing even meaning for the word science.

Dear Murugesan,

 I agree. There was a lot of invention that where crucial :

Jacobs’ staff, Astrolabe,Chorobate, Groma,The odometer by Vitruvius,The odometer by Heron... even balance scale :)

Dear @Amir, Viminacium is in my vicinity. I do find Roman Aqueduct as one of the greatest ancient engineering inventions of all time. I have attached one photo, see many of them by link given bellow.

http://viminacium.org.rs/en/arheoloski-park/akvedukti/

We should also mention some ancient computation devices such are:

The mesolabio of Heratosthenes  or The mechanism of Antikythera. The abacus  too. 

Interesting question and interesting answers.  Not sure the following 3 are considered ancient inventions in which they are still in use today:

1) fire - it helps us see in the dark, it helps us to be productive at night, it gives us warm and it helps the food tastes better

2) language / writing system - it helps our ancestors to record what they had experienced / learned & passed down to us as history / knowledge

3) raft / boat - it helps our ancestors to travel from island to island

Dear Han, as much as I should vote for the Cuneiform writing systems, as invented in Ur, in ancient Iraq, because it helps me communicate,  I must honestly vote for the invention of the boat because my most remote ancestor, Jean de Bettencourt sailed to discover the Canary Islands, in the 13th century, and I'm proud of this!!!

Dear Ljubomir! 

Herre's my favorite Aqueduct, a triple story one. From the South of Portugal, Elvas, near the border with Spain...

and the grand , splendurous Lisbon Aqueduct, that  I pass daily, on my way to work... (this was built, much later, in the 18th century, 

Portugal needs water desperately. This roman invention was providencial for my people and Country.

Science and technology in ancient and medieval India covered all the major branches of human knowledge and activities, including mathematics, astronomy, physics, chemistry, medical science and surgery, fine arts, mechanical and production technology, civil engineering and architecture, shipbuilding and navigation, sports and games. Ancient India was a land of sages, saints and seers as well as a land of scholars and scientists. Ancient India's contribution to science and technology include:

Mathematics - Vedic literature is replete with concepts of zero, the techniques of algebra and algorithm, square root and cube root. Arguably, the origins of Calculus lie in India 300 years before Leibnitz and Newton. 

Astronomy - Rig Veda (2000 BC) refers to astronomy. 

Physics - Concepts of atom and theory of relativity were explicitly stated by an Indian Philosopher around 600 BC. 

Chemistry - Principles of chemistry did not remain abstract but also found expression in distillation of perfumes, aromatic liquids, manufacturing of dyes and pigments, and extraction of sugar. 

Medical science & surgery - Around 800 BC, first compendium on medicine and surgery was complied in ancient India. 

Fine Arts - Vedas were recited and recitation has to be correct, which gave rise to a finer study of sound and phonetics. The natural corollary were emergence of music and other forms of performing arts. 

Mechanical & production technology - Greek historians have testified to smelting of certain metals in India in the 4th century BC. 

Civil engineering & architecture - The discovery of urban settlements of Mohenjodaro and Harappa indicate existence of civil engineering & architecture, which blossomed to a highly precise science of civil engineering and architecture and found expression in innumerable monuments of ancient India. 

Shipbuilding & navigation - Sanskrit and Pali texts have several references to maritime activity by ancient Indians.Sports & games - Ancient India is the birth place of chess, ludo, snakes and ladders and playing cards.

http://www.crystalinks.com/indiascience.html

https://en.wikipedia.org/wiki/List_of_Indian_inventions_and_discoveries

The dam was built by British Army Engineering corps under the supervision of Penny Cuick. The fund was stopped by the British as the under constructed dam was washed away by floods, and a second masonry dam was completed in 1895 with Benny Cook's personal fund as he had developed a intimate relationship with the people of the then Madras state.

http://archbhoo-india.blogspot.in/2012/04/mullaiperiyar-dam-tamil-nadu-cm-j.html

Let us go back to ancient engineering inventions, as @Amir asked for them. 

The inventions and technology of the ancient Greeks - you may see the first steam turbine, an ancient overhead crane, Archimedes hydraulic pump and many, many others.

The technological inventions presented here have been selected using the work of

Kostas Kotsanas, who has worked for over twenty years to make them revive. He rebuilt hundreds of machines and instruments that are now displayed at the "Museum of the Ancient Greek Technology" and the "Museum of Ancient Greek musical instruments and toys & games", located in Katakolon, the small port where cruise ships stop for the visit of the archaeological site of Olympia.

http://www.anticopedie.fr/download/technologies-gb.pdf

www.kotsanas.com

Dear Maria

On a lighternote about the wheel: I read somewhere that it is not the first wheel that was the greatest invention but the other three!

;-)

Narayanan

Dear Narayanan !!!

Yes, indeed... (You always make me think deeper!)

Nevertheless, you can travel higher and further with only one wheel if you get the proper imbalance !

Yes, Maria. You mean the Wheel of Life, which is single and we all ride it alone. Technology to philosophy. 

Narayanan

not only !!! But in fact, precisely that !!!

Ah, truly. All wheels of life are inside bubbles, A bubbly life I notice. Life is also a bubble, multicoloured depending on perspective. Who invented the first artificial bubble? It is also an engineering feat, isn't it?

Narayanan

Talking about wheel as an ancient engineering invention, let us remember  potter’s wheel that was used at Ur in Mesopotamia (part of modern day Iraq) as early as 3500 BC. The history of wheel follows!

http://www.ideafinder.com/history/inventions/wheel.htm

http://linoit.com/users/AshtonGriffith/canvases/Mesopotamian%20Wheel

http://www.ancient-origins.net/ancient-technology/revolutionary-invention-wheel-001713

Yes, Ljubomir. I also immediately thought of clay, and moulding, and the invention of writing on clay, from Ancient Mesopotamia...

What people call engineers' inventions are sometimes copies of what is found in nature?

Is the human invention of the needle to make cloths a copy of the beak of a bird building a nest?

But then why are there no wheeled animals?

http://biology.stackexchange.com/questions/7932/why-are-there-no-wheeled-animals

Dear @Marcel, many thanks for the page. 

"Wheels are possible on the molecular level — bacterial flagella are rotating cores inside a molecular motor, but wheels larger than this have not really been found..."

We, the engineers are always inspired by nature creations.

Dear Ljubomir,

But the ancient engineers did not have microscopes, I logically presume.

Cheers

Thus, if an invention cannot be a rough copy of what already exists (in nature), what is the definition of an invention?

Dear @Marcel, among many available definitions of invention, I am bringing two resources.

An invention is "the discovery or creation of a new material (either a new manufactured product or a new composition or matter), a new process, a new use for an existing material, or any improvements of any of these."

"New scientific or technical idea, and the means of its embodiment or accomplishment. To be patentable, an invention must be novel, have utility, and be non-obvious. To be called an invention, an idea only needs to be proven as workable. But to be called an innovation, it must also be replicable at an economical cost, and must satisfy a specific need. That's why only a few inventions lead to innovations because not all of them are economically feasible."

https://ipso.usu.edu/htm/inventors/whatisinvent

http://www.businessdictionary.com/definition/invention.html

Well, Dear Marcell

Just as a three dimensional being can postulate or write equation about a four dimensional structure but never construct, we too cannot construct any thing that is not already in Nature, even though we may think we did it. All inventions are re-descoveries even though we may take long to discover when nature made it first. TV, Radio, light bulb, Electricity, etc are all discoveries only and not true inventions.

So no real human-made inventions, except may be Language, which is not a physical property (even though articulation etc, are physical). But then Nature invented us and through us Language.

Narayanan

Dear Narayanan,

Language is common in nature, but perhaps not the way language is organized. If new words are used, are that really inventions or culture-based mutations or copy errors or...?

I meant that only humans have the "Faculty of Language' which is lacking in all other animals. But then again, this is Natures gift to human kind (or rather woman kind?). So it also is natures invention, eh. So new words also come into this, and is in our nature.

Narayanan

 To add to this interesting discussion the Archimedes' principle of buoyancy (specific gravity) as the greatest - yet it is so difficult to explain and to get it understood, but has so many applications.

There may be no greater tribute to a society's ingenuity and vision than Egypt's Great Pyramid of Giza. Originally standing 481 feet (147 meters) tall, the Great Pyramid towers over monuments like the Statue of Liberty and Big Ben. Of course, the pyramids are only part of ancient Egypt's legacy.

http://science.howstuffworks.com/innovation/inventions/5-amazing-ancient-egyptian-inventions.htm

 Virtual reconstruction of the water clock by Ctesibius

 Virtual reconstructions of Heron’s dioptre (left) and of a Stadia (right).

Another example, inspired by @Amir! 

Virtual Reconstruction Reveals Secret to Ancient Sundial!

"Scientists have used latest technology to produce virtual simulations of an Egyptian obelisk and the famous Ara Pacis (Altar of Peace) in ancient Rome to solve a mystery surrounding the ancient obelisk, which functions as a giant sundial. The 3D reconstruction they produced shows how the sun would have lined up with the obelisk and the altar.

http://www.ancient-origins.net/news-history-archaeology/virtual-reconstruction-reveals-secret-ancient-sundial-001186