A long time ago I needed a Celtic-looking border for a design I was doing, but it needed to be circular. Instead of trying to calculate the points of intersection around a circle, I simply made myself a brush, created a circle of approximately the size I wanted, and applied it. Presto! Instant Celtic border.

Now you too can have fun with this. It's an Illustrator pattern brush that includes mid-sections, corners and end-sections.

[EDIT] Now includes corner pieces. Download the new Illustrator file for even more versatility.

[EDIT 2] By request, I’ve included versions in Illustrator native format (.ai) and EPS (.eps). You’ll still need Illustrator CS2 or newer to use the brush, but the pieces that make up the sections are available as expanded elements in the EPS version.

To use this, download the link and open the file from the flyout menu in the Brushes pallette. For extra added convenience, you can place the file in your Illustrator > Presets > Brushes folder and it will be available in the main list of brushes, instead of you having to hunt for it.

Lastly, if you find this useful, I'd love to see what you create with it.

[NEW] Apparently, this is being featured off-site: Vector Art on Blogspot.com. Not a bad little resource site.