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Wooden sledges are first known, by at least 7000 BC, among communities living by hunting and fishing in northern Europe, on the fringes of the Arctic. It is possible that they use dogs to pull them, but the technological advance is valuable even without animal power.
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A wagon gets stuck in the mud, more than 5000 years ago, near what is now Zürich. It has two pairs of solid wooden wheels, each attached to an axle which turns with them. The wagon is massively heavy (perhaps about two thirds of a ton, or 700 kg) and it is irretrievably stuck. It stays where it is. It is now one of the earliest known examples of wheeled transport.
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Carriages are available for hire in the streets of London from 1605. By the second half of the century there are traffic jams.
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The modern trailer
