The post led me to wonder what historical commemorations could be held in a fictional world. Yes, there could be anniversaries of great battles but what if your world is generally a peaceful one? What does it find important enough to commemorate?
Are there civic events the entire realm/country remembers or just local ones? Your fictional world must have some history behind it which has shaped how and why it is the way you've written it. So bring some of this into your stories.
What people/beings lead historical commemorations? Do these unite people? Is history deadly serious or fun (or a bit of both? I love serious history but also appreciate things like the Horrible Histories series, which can be a great way of getting youngsters into history at all).