Nov 5th 2008 9:57AM Now pay attention here, I'm going to give you an Ancient Greek lesson free of charge.
In Ancient Greek, there are 'cases' - nominative, genitive, dative and accusative. Most of the time, the plural of the nominative is used for normal words in English.
The nominative singular of πόλις (pólis) is of course, πόλις. Now I'm not gonna bother with all the cases, but here's the nominative plural for good measure: πόλεις (póleis)
Now because necropolis comes from Greek, the plural is necropolEIS. Got it? Good.