query: When was the train first invented?
passage: History of rail transport
The first full-scale working railway steam locomotive was built in the United Kingdom in 1804 by Richard Trevithick, a British engineer born in Cornwall. This used high-pressure steam to drive the engine by one power stroke. The transmission system employed a large flywheel to even out the action of the piston rod. On 21 February 1804, the world's first steam-powered railway journey took place when Trevithick's unnamed steam locomotive hauled a train along the tramway of the Penydarren ironworks, near Merthyr Tydfil in South Wales.[28][29] Trevithick later demonstrated a locomotive operating upon a piece of circular rail track in Bloomsbury, London, the Catch Me Who Can, but never got beyond the experimental stage with railway locomotives, not least because his engines were too heavy for the cast-iron plateway track then in use.[30]
passage: Uruk period
A debated question in the realm of transport is whether it was in the Uruk period that the wheel was invented. Towards the end of the Uruk period, cylinder seals depict sleds, which had hitherto been the most commonly depicted form of land transport, less and less. They begin to show the first vehicles that appear to be on wheels, but it is not certain that they actually depict wheels themselves. It remains most likely that the wheel was invented in the northern Caucasus (Maykop culture) or Eastern Europe (Cucuteni-Trypillian culture), where the most ancient surviving examples have been found. In any case, the wheel spread extremely rapidly and enabled the creation of vehicles that enabled much easier transport of much larger loads. There were certainly chariots in southern Mesopotamia at the beginning of the 3rd millennium BC. Their wheels were solid blocks; spokes were not invented until c. 2000 BC.