If you'd only like the content to live at one location, and you're worried about legacy links that people shared across the internet breaking, then a 301 redirect from the old URLs to the new URLs is what you're looking for.

Every HTTP Request receives a response code from the web server. Response codes in the 200s mean "everything went well", response codes in the 400s mean "user error" (like the famous 404, "we couldn't find the page you requested") and response codes in the 500s mean server error (Twitter's famous 503 Fail Whale).

300s indicate some sort of redirection and a 301 response code specifically tells the requesting client that this piece of content has moved to a new URL *permanently* and will never be back at this old URL.

When web browsers receive a 301 redirect, they'll cache it and automatically forward all future requests for the old URL to the new one without even asking the server. Similarly, when search engine crawlers encounter a 301 redirect for a URL that they had already indexed, they update their information to move that old content (and all of it's old ranking information) to the new URL. This means you don't have to "start over" to get a piece of content to rank if you move its URL.

However, your question makes it sound like you actually *do* want the exact same content to be served out of multiple URLs, but you'd ideally like only one copy of that content to be indexed and ranked to avoid splitting your inbound links and any other duplicate content issues.

In that case, I'd check out adding so called "rel-canonical" tags to your pages, to indicate which version is the "canonical" version of that piece of content, and have all other versions point to the canonical one with the tag. Google is pretty good about using these, and Bing says they use it has a "hint." More info:

https://support.google.com/webmasters/answer/139394?hl=en

In a world where websites might choose to organize the exact same content in a number of different ways, adding "rel canonical" tags to your pages adds a lot of semantic meaning and helps you avoid a number of issues that duplicate content brings. Hope that helps!