I am building a garden bridge with an arch which is part of circle that has 25 foot radius.
The bridge is only 12 feet long over the arch. Because the radius is too long for my work area I would like to know, other than using a stringline to transcribe it onto timber, if there is any other method of making a template to do the job. Any help please ?

There is a mathematical solution, of course, but I would lay it on a piece of paper in a parking lot.

I wrote an excel program to do this for some interior arches. It'll tell you the height off vertical for any point on the arch.

Let me know by pm if you are interested, and I'll send it to you by e-mail.

Thanks for the responses but I want to avoid using stringlines, and I know the height of the chord. I was just wishfully hoping for an easy way to make a template, but thanks anyway.

Spring a batten, maybe?