I was thinking about how old some buildings are in New York... then missions in New Mexico... then wondering what the castle was that Newcastle was named for.
How long have we named places after other places? Will someone build a "New New York" (or even a "Nuevo Nova Scotia") on Mars someday, or has the moment of naming places New-wherever passed?
Cartagena is the modern version of "Carthago Nova," i.e., "New Carthage"; the name dates from the Roman conquest (209 BC) although the city is older.
Carthage itself means "New City," but that's not the type of "new" you're looking for.
When Constantine refounded the city of Byzantium to be his new capital, Constantinople, it also took on a name of "Nova Roma", or New Roma, which seems to be something more than a nickname and less than the official name. The Patriarch of Constantinople (the head of the Eastern Orthodox church, though less directly than the Pope is head of the Catholic Church) is still technically "His Most Divine All-Holiness the Archbishop of Constantinople, New Rome and Ecumenical Patriarch".
Seriously, Istanbul might hold the record for most different names for a city. New Rome is just one of the minor names for it.
Naples in Italy has a name deriving from the Greek Νεάπολις ("new city"). It was founded around the sixth century BC by colonizers from the older settlement of Cumae.
Source: Hughes et al (eds), Remembering Parthenope: The Reception of Classical Naples from Antiquity to the Present
As a follow up question, are there any "New" cities that still have the "new" part of their name as a distinct word or particle? I've noticed that in some of the answers here, the "new" component has long since been absorbed into the parent word.
The castle at Newcastle is this one http://www.newcastlecastle.co.uk/ named as such because it replaced the old castle. It was called Monkchester until its destruction in the "Harrying of the North", then Novum Castellum when a new castle was built there in the 1080's.
Bonus question: why is New York called such. I thought it was named after the Duke of York (not 'old' York), so why the 'New'?
then wondering what the castle was that Newcastle was named for.
It depends which Newcastle you're talking about, there are 7 Newcastles in the UK, including the big city Newcastle Upon Tyne. The settlements developed around castles so were named after them, most of which are still extant. If it's one in the US then it's most likely named after one of them, so probably would be considered 'New Newcastle'