I get the general idea that a city will build upon itself but mechanically, how does it happen exactly? People tossing out their lettuce cores and carrot peelings and animals crapping can't be responsible for it all, can it? Physically bringing in fill dirt would be a huge undertaking.
I can understand it for a city on a floodplain like Cairo but not so much for a city like London. Learn me on this process and if there are any books on the subject worthy of mention, mention them.
Hi, this is more of an archaeology question, so you might consider x-posting to /r/Archaeology, /r/AskAnthropology or /r/AskScience for more feedback/source recs. Meanwhile, this question comes up occasionally here, so you can check these out. They will give you at least a few usernames to followup with, if not also some source refs.
Layers
Why did the Romans build on top of things? - featuring /u/kookingpot
Many archaeological sites of settlements are often described as having "layers". Are these literal layers or an archaeological term? - featuring /u/Aerandir
Buried ruins
Why does so much archaeology end up underground? - featuring /u/kookingpot and /u/alriclofgar
How did ancient archaeological sites like the Palace of Knossos and Troy (but not limited to) get buried? - featuring /u/mictlantecuhtli
Archeologists are always digging up ancient ruins. How did all of these ruins get buried in the first place? - featuring /u/Pachacamac and /u/Tiako
of possible tangential interest