A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
From a drawing in 'From Snowdon to the Sea. Striking stories of North and South Wales', Marie Trevelyan, 1895.
Source Firkin
Zero CC tileable moss or lichen covered stone texture, edited from pixabay. CC0
Source Sojan Janso
Remixed from a drawing that was uploaded to Pixabay by captenpub.
Source Firkin
Prismatic Geometric Pattern Background No Black
Source GDJ
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Lovely pattern with splattered vintage speckles.
Source David Pomfret
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.
Source Firkin
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
Sharp pixel pattern, just like the good old days.
Source Paridhi
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Prismatic Hypnotic Pattern No Background
Source GDJ
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
Inspired by an image that was uploaded to Pixabay by geralt
Source Firkin
Background pattern made in "Grunge-Like" style. Available in both SVG and JPG formats. Edit to your needs then click the download button.
Source V. Hartikainen
A floral background formed from numerous clones of flower 117.
Source Firkin
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
From a drawing in 'Hyde Park from Domesday-Book to date', John Ashton, 1896.
Source Firkin
Green Web Background, Seamless tile.
Source V. Hartikainen