The region in which "Cockneys" reside has changed over time, and is no longer the whole of London.
A common belief is that in order to be a Cockney, one must have been born within earshot of the Bow Bells. However, the church of St. Mary-le-Bow was destroyed in 1666 by the Great Fire of London and rebuilt by Sir Christopher Wren. After the bells were destroyed again in 1941 in The Blitz of World War II, and before they were replaced in 1961, there was a period when by this definition no 'Bow-bell' Cockneys could be born. The use of such a literal definition produces other problems, since the area around the church is no longer residential and the noise of the area makes it unlikely that many people would be born within earshot of the bells anymore.
A study was carried by the city in 2000 to see how far the Bow Bells could be heard, and it was estimated that the bells would have been heard six miles to the east, five miles to the north, three miles to the south, and four miles to the west. According to the legend of Dick Whittington the bells could once be heard from as far away as Highgate. The association with Cockney and the East End in the public imagination may be due to many people assuming that Bow Bells are to be found in the district of Bow, rather than the lesser known St Mary-le-Bow church.