Redwall

[Vilu Daskar]

Did you know that Redwall Abbey was built over Castle Kotir? It's in The Long Patrol.

Yes, now you mention it - was there a ditch mentioned in Mossflower? That might explain it. Perhaps it was a moat of sorts for the old castle, or... or something?

But the ditch follows the path all the way to river moss.

[The Skarzs]

Revive. Yeah, old topic, but I'd just like to put in my two cents on the matter.

Ever since I heard about the ditch when I read the books, I had always assumed that it was made there for a couple reasons: First, to provide the material to make the path. When a road or anything is made, extra dirt and stuff is added to fill in low spots, as well as putting another layer on top for when it is compacted; roads must be packed down so as to stay sturdy enough for travel. Secondly, the ditch would let rain drain off toward wherever it lead, keeping water from ruining the path/road.

[Tam and Martin]

Totally agree there. Back in their time, they didn't have cement or concrete so they would have to compact the dirt down so it would be safe to travel on.

[Captain Tammo]

Yeah good point there, Skarzs.
I strongly doubt that the Redwallers put in the ditch just to use as defense since they always had the safety of their walls to be behind. If it was put there for defense, that would be a pretty lousy call on the architect's part seeing as how every horde that lays siege to Redwall uses the ditch as cover. Perhaps that's it!!

You see, Brian never specifically tells us why the ditch is there, right? In the first book, Redwall, the ditch is simply shown as being there. But consider this, I think Brian wanted a creative way to shield the villains from fire up on the wall tops, so he just... Made the ditch a thing to spice it up a bit! Could you imagine how easy it would have been for Redwall to be defended if there was no ditch for villains to hide behind? it'd be almost boring! I also think that maybe Brian included the ditch so that you couldn't have things like siege towers coming straight at the wall. The ditch ends up serving as an interesting environmental advantage and disadvantage on both sides of the fight.

Then, as the series moves along, we see that the ditch appears to be something that stretches up and down the path a ways. I don't recall if this was something mentioned in Redwall, but I think Brian just added a little bit where it became a much bigger ditch than in the first book, serving as all kinds of things, mainly trash and a sort of drainage system for the local area.

So to summarize, perhaps the ditch was just a thing that Brian added because he could? Then it went on to serve a bunch of functions and play a surprisingly big role in the series.