I guess this is inspired by the city of Ravenna in Italy and its stone walls.
Source Sentel
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
The file was named striped lens, but hey – Translucent Fibres works too.
Source Angelica
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay
Derived from a drawing in 'Elfrica. An historical romance of the twelfth century', Charlotte Boger, 1885
Source Firkin
We have some linen patterns here, but none that are stressed. Until now.
Source Jordan Pittman
It’s a hole, in a pattern. On your website. Dig it!
Source Josh Green
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
Remixed from a drawing in 'Works. Popular edition', John Ruskin, 1886.
Source Firkin
Formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
You know I’m a sucker for these. Well-crafted paper pattern.
Source Mihaela Hinayon
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.
Source Firkin
A repeating gloomy background image. This one consists of a pattern of black chains layered on top of a dark textured background.
Source V. Hartikainen
This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Here's a brown background pattern with subtle stripes. I hope you'll like the color. If not, feel free to change it using an image editor, if you know how of course. Personally, I'm using GIMP to create these backgrounds.
Source V. Hartikainen