Excel Help - sorting dates

[rokerexile]

I am trying to sort some data in excel by dates (dd/mm/yyyy) but it is just looking at the dd bit and not sorting by the date as a whole. For example, if I have a date of 13/02/1834 and a date of 20/03/1776 and I want to sort by earliest date first I get the wrong result because 13 is earlier than 20 and it ignores the rest. Anybody know how to solve this, I'm a bit rusty with Excel?