Rahul Mehta Gandhinagar LsCandidate

Can level engineering skills and total ability of society as a whole decease or can only increase?
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Consider nation or whole world. Lets say that nation or world has certain level of engineering skills and achievement. eg say it can build road of certain quality and say it is capable of building say X km of roads every year
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Then due to natural calamity or war, this sum total ability may go down down a few year. But can it go down in long run? Shoundt next generation be always better -- more skilled and more resourceful -- that previous generation? After all, even if next generation doesnt add any new innovation, then also it will be able to preserve the existing inventions / discoveries and maintain them.
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So as such it appears that next generation should always be more skilled in engineering than previous one.
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But not so
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Romans could make roads in 100 BC and upto 300 AD, and later Europeans could NOT make such roads for next 1300 years !!! And likewise, Romans could make aqueducts to carry water, pipelines etc which Europeans could not make for next 1300 years.
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Are such examples in other parts of world?
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So what factors led to LOSS of skills and sum total of abilities? How can sum total of abilities and sum toatl of skill reduce? The reasons may be different for different society and time,. What could be reason for fall of skills in Europe? And other places where it may have happened?