By the middle of the 1800s, London had all but exhausted its potential to bury it's dead. Churchyards and burial grounds alike were overflowing and no sooner were the dead buried, then they were dug up again to make room for the next new arrivals. Places like Spa Fields were 'burying' more each year than had been originally expected in their entire lifetime.
The situation became so bad that a 1832 Parliamentary Act was passed to allow the establishment of seven private cemeteries in a ring around what was then the outskirts of London, to take over the responsibility for London's burials. They were by the existing London standards both large and initially spacious, and are known today as the 'Magnificent Seven'. In an age when it was the norm to bury the dead in the style and custom which would befit the deceased, it became to be seen as a mark of wealth and status to pay for 'a good funeral' and then to erect grand monuments to the dead afterwards.
Today much still remains of this extravagance and after being left for decades to the effects of both nature and vandalism, they are now being increasingly seen as a heritage that needs to be preserved.