Once upon a time, people walked the earth, not taking apart roads. Then there was no such word - “road”. Later, when a man tamed a horse, he at the same time realized that it was best to ride on the same trodden place. Then came the wagons, which moved on rails - horse-drawn, and then electric trams. By this time, the people on the streets of big cities were not crowding. It was decidedly impossible to get somewhere on time.
And in the middle of the nineteenth century, a brilliant idea came to the head of an engineer living in London: to build roads underground. Dig tunnels there and run a train along them. At first, the Londoners did not succeed - the unfinished tunnel under the River Thames was constantly flooded with water. But they were stubborn people, and in 1863 the first trains set off on an underground highway. And since it was built by a company called the Metropolitan, it was then that they began to call subways around the world. And at first it was not very convenient to ride the subway - the smoke from the engine filled the cars, making people cough. But over the years, new transport has become better and better.
Now there is a metro in almost every big city. In Russia, the first metro opened in Moscow in 1935. It was incredibly difficult to build, because under the metropolitan streets met underground rivers and quicksand - huge strata of sand saturated with water.
And now they dig tunnels with the help of special tunneling shields. This machine resembles a huge steel worm: its teeth are incisors in front and a mechanical arm in the back, which puts in a row cast-iron or concrete rings. Of these, it turns out the subway tunnel. Then they lay rails in it, stretch the electric wires so that there is something to feed on the train - and go!