There are bales of straw hanging from the Thames bridges. It is not a coincidence, it is a centuries-old security system

If you visit London, you may have seen that a huge bale of straw hangs from some bridges that cross the River Thames. Nobody has left it there by mistake, it is a signaling system that dates back to the 18th century.

Notice to sailors. The reason for hanging a bale of straw from the bridges that cross the Thames comes from an old regulation of the port of London. Clause 36.2 of the statutes indicates that a straw bale must be hung “when the free height of an arch or the span of a bridge is reduced with respect to its usual limits”, that is, it is a signal so that no boat hits the bridge.

Dubious effectiveness. When the law was first enforced it made sense to use some physical element as a warning that a bridge was lower than usual. At that time, the Thames was the main access route for goods to the city and it was very busyso it was necessary to use signage. What is striking is that it has been maintained over the centuries, especially considering that there are more effective methods to mark it, especially at night when the bullet may not be clearly visible.

Recent cases. It is not a rarity, the system is applied religiously whenever there is any work that reduces the height of a bridge even a little. Happened in 2023 on the Millenium pedestrian bridgein 2024 in the East India Dock Road Bridgein 2025 in the Barnes Railway Bridge and in the Charing Cross Bridge. Those responsible for hanging the straw bale are the contractors who carry out the corresponding work. If they don’t, they face fines of up to £5,000.

A very English custom. There are more quaint laws still in force in the United Kingdom, such as the one that states that certain species of fish are property of the crown (whales, dolphins or sturgeons) or the ‘Salmon Act’, which establishes as a crime the “suspicious handling of a salmon”, in reference to poaching. There are others that for whatever reason do not continue to apply, such as Licensing Act of 1872 that prohibited being drunk in a public place.

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