Building an Arched Wooden Bridge

I made this garden bridge in March 2002 and it is still standing strong today.
The free plans and instructions for this project were first posted on the BuildEazy website on the 23rd April 2002.
Since then, the online format has been changed a couple of times to suit evolving website design - but the original
instructive in essence is pretty much as it was.
Introduction, navigation & wood sizes
This bridge spans 2100 mm (7ft) and is 680 mm (27") wide.
Not only will it become a feature in your garden, but it is strong enough to serve a practical
purpose as well.
It could well be incorporated into your garden path system.
This particular bridge was constructed entirely on the back lawn, showing that you do not always
need an elaborate workshop or shed to undertake such a project.
Navigation
Jump around the pages via the 'Table of Contents' in the right-hand sidebar or jump to individual steps via the 'thumbnail pictures' directly to the right.
Wood sizes
The measurements throughout this project are given in both Metric (mm) and Standard/Imperial inches.
The metric measurements (mm) are given first followed by the imperial measurements (inch) in brackets ().
There are only two stock sizes required for this project, both being common stock sizes.
They are...
90 mm x 45 mm (1 1/2" x 3 1/2") and 90 mm x 19 mm (3/4" x 3 1/2").
90 mm x 45 mm means wood that is 90 millimetres wide by 45 millimetres thick.
That is called the actual size.
The nominal size of the wood relates to its size prior to being dressed (planed, surfaced, smoothed).
For example, wood that is 100 mm x 50 mm (nominal size), becomes 90 mm x 45 mm (actual size) once it has been dressed (planed, surfaced, smoothed).
And the equivalent in standard...
1 1/2" x 3 1/2" means wood that is 1 1/2 (one and a half) inches thick by 3 1/2 (three and a half) inches wide.
That is called the actual size.
The nominal size of the wood relates to its size prior to being dressed (planed, surfaced, smoothed).
For example, wood that is 2" x 4" (nominal size), becomes 1 1/2" x 3 1/2" (actual size) once it has been dressed (planed, surfaced, smoothed).
Note:
The 90 mm x 19 mm (3/4" x 3 1/2") boards used for making the arches must be premium and knot free. If there are any deformities in the boards, then they may snap when bending pressure is applied.