This method of making arches is considered by many to be the most efficient way because it creates less sparklies as opposed to the end cap method. Its up to you which method you want to use, though this method is considered the best.
First up lets sort out where the arch needs to be placed. Ive made a simple tunnel, fig 1.0
Now we need to create a brush for the first bevel, this is going to be half of the arch. So create it half way across the width of the tunnel, as shown in fig 1.2 and fig 1.3
Now with your brush selected go to "curve" and then chose "bevel" from the toolbar.
It will now create a bevel out of the brush, fig 1.4
(Fig 1.4) As you can see its not facing the correct way or at the right angle, what we need to do is rotate it using the rotate buttons, fig 1.5
Ive had to press the X>x button, its then facing the right way, so I have then moved it into position on the right side of the tunnel, fig 1.6, 1.7 and 1.8
You can see that the face or texture is facing the wrong way (see fig 1.6).
What we need to do here is go to "curve" then "matrix" then chose "invert" it will
then move the face to where we need it, fig 1.7
What we now need to do is stretch out the piece so its the length of the tunnel, the texture will stretch as well though, so what we need to do now is make the texture go natural. To do this select the piece of arch and then press "s" to bring up the texture applicator, and then press the "natural" button and then "done" (you can also use the curve texture applicator for some texture movement, to use that press shift and s)
Go to "curve" and then "cap selection" and a window will pop up, fig 1.8
The parts in blue are the parts that will be the new brushes/patches,
although our arch is facing the other way to that of the picture,
we need an inverted bevel, you can see it is the same shape
as our half arch only facing the other way, it doesnt matter
that its facing the other way in the picture, it will make it
properly, so choose "inverted bevel" and then press
"ok", fig 1.9, fig 2.0
You can see that the texture on the front has actually aligned up, so theres no need to align it, if it doesnt align up for you, try using the curve surface inspector (hold shift and press s)
we have half an arch. Before we copy it, ive stretched mine
out to the length of the tunnel. All you then need to do is
select the arch piece and press "space" to copy and
paste it and then you need to press "x|x" on the toolbar
for it to rotate to face the correct way. Then you need to move
it into place, or move it into place and then press the "x\x"
on the toolbar, its up to you, as long as you now have a full
arch, fig 2.1
need to caulk behind the arch where you cant see, as we can
see our arch doesnt go all the way to the floor so we need
to make some more brushes. See fig 2.2 and 2.3
First lift up the 2 walls and then add some new walls below them, fig 2.3