Are the logs in /var/log/ automatically rotated?

[Don Bedsole]

Hi,
I was wondering if the logs in the /var/log directory 
(especially /var/log/messages) are automatically deleted after a certain 
period of time or when the log file gets to a certain size.  Or, is this 
something that needs to be set up manually by the user using a cron job or 
something like that?  I have just changed my iptables rules to include some 
logging and the messages go to /var/log/messages.  I'm not too worried about 
getting my hard drive filled up with log messages, but I don't want to save 
them forever either. Thank you.
-- 
For God so loved the world, that he gave his one and only Son, that whoever 
believes in him should not perish, but have eternal life.
(John 3:16, WEB)