Britain is really old and this means that it’s that were dreamt up centuries ago and never updated. Now, one such law is proudly on display in London where are hanging a bale of hay from their worksite.

Workers making repairs to the Millennium Bridge in central London have been forced to suspend a bale of hay below the bridge while they make repairs to the site, according to . If that sounds like a rogue move, it’s because it is, but it’s all to do with a centuries-old bylaw that’s enforced across London, as the Guardian explains:

Repair works to the footbridge mean straw must be dangled to warn oncoming boats of the work going on beneath it.

The large bale, which these days is lowered on climbing rope by workers in hi-vis jackets, is intended to alert river traffic of the reduced headroom.

The law only impacts bridges spanning the river Thames in London, and it last when repairs were being made to Wandsworth bridge further up the river. According to the Port of London, the weird law is part of its Thames River Bylaws, which were last updated in 2012. The bale of hay is a hold over from much earlier versions.

Despite being brought up to with the addition of rules governing things like hydrofoils on the Thames and where you can or can’t land a seaplane on the river, the hay bale law remains in place. In fact, it’s one of two bylaws about hanging stuff from bridges in London, with the second stating that three large red discs should be suspended below a bridge when it’s closed to traffic. The hay bale law itself states:

“When the headroom of an arch or span of a bridge is reduced from its usual limits but that arch or span is not closed to navigation, the person in control of the bridge must suspend from the centre of that arch or span by day a bundle of straw large enough to be conspicuous and by night a white light.”

In the bylaws, it’s also joined by another rule that stipulates that on the Thames must have the word “ferry” painted on the side. Other fun London laws that you might not know also include one that states that certain buildings around London must always have an uninterrupted view of St Paul’s Cathedral.

This Protected Views law is the reason that got its cheese grater shape. London, what a weird old place.