Why is this MVC route incorrect? - asp.net-mvc

Question

In my MVC application's RouteConfig I am using this:
routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);
routes.MapRoute (
name: "Dictionary", // Route name
url: "dictionary/{id}", // URL with parameters
defaults: new { controller = "Dictionary", action = "details" } // Defaults
);
At this time this URL succeeds in returning a page:
http://127.0.0.1:8080/dictionary/details/1
Whereas this fails:
http://127.0.0.1:8080/dictionary/1
With the exception
"HTTP 404.The resource you are looking for (or one of its dependencies) could have been removed, had its name changed..."
When I swap the routing around, like this:
routes.MapRoute (
name: "Dictionary", // Route name
url: "dictionary/{id}", // URL with parameters
defaults: new { controller = "Dictionary", action = "details" } // Defaults
);
routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);
It both URLs start returning a page.
Why is this?
Thanks in advance.
FYI This question is different to the possible duplicate because of the UrlParameter.Optional and the wild carded routing in the other question. This question is more about which specific ordering is correct and why.

Answer 1

The order of the routes that you add to the route table is important. If you reversed the order, then the Default route always will get called instead of the custom route.
Reference:
https://www.asp.net/mvc/overview/older-versions-1/controllers-and-routing/creating-custom-routes-cs