Does the frequency of sex go down drastically in a marriage of many years?

A good portion of the media would have us believe that marriage is synonymous with celibacy. As far as I know, this is not true but as I am not, nor have I ever been, married and since my mother has never been married, I do not for sure. I know it is relatively common for couples, whether married or not, to have less sex as time goes on, but I’m hoping the people who are married or were married at some point to inform me.

So, married people, do you have a lot less sex than you did in the beginning of your relationship?