The page http://arduino.cc/en/Main/ArduinoBoardMega2560 refers to:
Schematic, Reference Design & Pin Mapping
Pin Mapping: PinMap2560 page
... where this PinMap2560 page links to http://dev.arduino.cc/wiki/en/Hacking/PinMapping2560; going to that link results with login and password being asked; the current arduino.cc login and pass fail with:
401 Authorization Required This server could not verify that you are authorized to access the document requested. Either you supplied the wrong credentials (e.g., bad password), or your browser doesn't understand how to supply the credentials required. Additionally, a 401 Authorization Required error was encountered while trying to use an ErrorDocument to handle the request.
Trying to remove 'dev' and call directly http://arduino.cc/wiki/en/Hacking/PinMapping2560 results with:
That thing you are looking for is not here, dude! Server error code 404
Is this a server configuration error - or is that link not intended to be public?