This nondescript bollard looks like any other streetside safety feature. Millions of people pass by its busy Princes Street location without realizing its historical and geographical meaning.

The bollard doesn’t denote the true geographical center of Edinburgh. Instead, it marks the location of the original Edinburgh General Post Office.

All postal codes radiate outwards from the bollard. The post was also used as a marker to gauge all distances to and from the city. Additionally, all street numbers begin at the end of the street that’s closest to the bollard.

The old post office wasn’t the only interesting feature to stand at this site. The building originally hosted The Theatre Royal, which was constructed between 1861 and 1865. The principal architect behind the Italian Renaissance building was Robert Matheson, who was also the mastermind behind many of New Town’s important structures, like the General Register Building of the National Archives of Scotland.