What name is given to the unpaved road along the south side of London's Hyde Park, normally reserved for Horseriders?

Rotten Row is a broad track running for 1,384 metres (4,541 ft) along the south side of Hyde Park in London. It leads from Hyde Park Corner to Serpentine Road. During the 18th and 19th centuries, Rotten Row was a fashionable place for upper-class Londoners to be seen horse riding. Today it is maintained as a place to ride horses in the centre of London, but it is little used. Rotten Row was established by William III at the end of the 17th century. Having moved court to Kensington Palace, William wanted a safer way to travel to St. James's Palace. He created the broad avenue through Hyde Park, lit with 300 oil lamps in 1690– the first artificially lit highway in Britain. The lighting was a precaution against highwaymen, who lurked in Hyde Park at the time. The track was called Route du Roi, French for King's Road, which was eventually corrupted into "Rotten Row".

In the 18th century, Rotten Row became a popular meeting place for upper-class Londoners. Particularly on weekend evenings and at midday, people dressed in their finest clothes to ride along the row and be seen. The adjacent South Carriage Drive was used by society people in carriages for the same purpose. In 1876, it was reconstructed as a horse-ride, with a brick base covered by sand.