The novel's 'sepulchral city' is based on Brussels (see Setting), the capital of Belgium.
The phrase 'whited sepulchre' comes from Matthew 23:27-28:
Woe unto you, scribes and Pharisees, hypocrites! for ye are like unto whited sepulchres, which indeed appear beautiful outward, but are within full of dead men's bones, and of all uncleanness. Even so ye also outwardly appear righteous unto men, but within ye are full of hypocrisy and iniquity.
The original typescript continued with a more detailed description: ‘Its quiet streets empty decorum of its boulevards, all these big houses so intensely respectable to look at and so extremely tight closed suggest the reserve of discreet turpitude.’