From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
Heavily remixed from a drawing that was uploaded to Pixabay by ractapopulous
Source Firkin
From a drawing in 'Studies for Stories', Jean Ingelow, 1864.
Source Firkin
A light gray fabric pattern with faded vertical stripes.
Source V. Hartikainen
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
Not the Rebel alliance, but a dark textured pattern.
Source Hendrik Lammers
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
Prismatic Hexagonalist Pattern No Background
Source GDJ
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Lovely pattern with splattered vintage speckles.
Source David Pomfret
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Colourful background achieved with gradient fills.
Source Firkin
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin
Turn your site into a dragon with this great scale pattern.
Source Alex Parker
This is sort of fresh, but still feels a bit old school.
Source Martuchox
Prepared mostly as a raster in Paint.net and vectorised.
Source Firkin
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers