In addition to the other answers, which clearly and correctly identify the suffix –poli as meaning city, I would like an interesting historical point. The suffix can be used in two different ways:
- in common words, like baraccópoli;
- part of proper nouns, like Napoli or Costantinopoli.
Tangentopoli originally was an example of 2., because it was a nickname for Milan ("City of bribes"). Paperopoli is also another example of use in this sense.
After the corruption scandal became such a huge issue, the meaning of the suffix actually changed, and is now used in a manner similar to the English –gate suffix, which started with a proper name (Watergate) and was then extended to many other scandals.
In this sense, –poli is used in common words now, an usage which is called accidental usage, but it has lost the meaning of city, just like –gate has lost any geographical connotation. It just means large scandal.
A funny side note. The proper noun of the game Monópoli is pronounced with a second-last vowel accent like a proper city name. This is to imitate the English game name of Monopoly. In reality, the word monopólio does not use the suffix –poli but the suffix –polio which means vendor. In fact, the old spelling of the plural monopóli should be monopolii, monopolĳ or monopolî.
Normally, in Italian –poli never takes an accent.
- Treccani, -Poli, Vocabolario on line