The London Stone was once considered to be one of the City’s most important relics with the very existence of the city depending on its survival. Yet, hidden away behind an iron grille set into the front of a building at 111 Cannon Street, the block of Clipsham limestone is these days all but forgotten, occupying an ignominious position opposite the gleaming new Cannon Street Station.

The stone’s origins lie shrouded in mystery but the legend, propagated in the 19th century, goes that it once formed part of an altar built by Trojan wanderer and founder of London, Brutus. Yet, according to the Museum of London, the saying often associated with the legend  – “So long as the Stone of Brutus is safe, so long will London flourish” – was apparently invented in 1862.

It has been suggested the stone, which is a Grade II* listed structure, may be a relic of the city of the Roman city of Londinium, although no-one seems to know for sure. The earliest mention of it was apparently around 1100 AD and it was subsequently associated with some of London’s most famous characters.

It is said that Jack Cade, leader of the 15th century Kentish rebellion, struck it with his sword after entering London in a symbolic gesture designed to reflect his taking control of the city and naming himself ‘Lord of London’. The poet William Blake is said to have believed it to be associated with druidism – perhaps it was part of an altar? – and even the great 17th century architect Christopher Wren had a view on it – he thought it was part of a Roman ruin after seeing its foundations.

One widely believed and circulated theory was that it was the stone from which all distances from London were measured during Roman times. Its heritage listing says it may have been a Roman milestone. It has also been suggested it is the base of an Anglo-Saxon waymarker or cross.

The stone was located in its current position after World War II. Since the 18th century it had been set into the wall of a Wren-designed church, St Swithin London Stone, which had stood on the site where the stone now sits but which was demolished in 1962 after being bombed in the Blitz. Prior to being moved to the church, the stone stood upright on the south side of Cannon Street. It was moved to the church after becoming a traffic hazard.

There has been talk in recent years of moving the stone to a better home but for the moment it remains behind the grill by the footpath.