Thanks so much! That's a great site.

This is the site I found this morning: http://www.kinnaird.net/tartan.htm

Here is the relevant part:

It is impossible to say precisely when the tartan cloak evolved into the long garment known as the belted plaid (and which itself was the forerunner of the modern kilt), but it was probably around the tenth or eleventh centuries. This long plaid was wrapped round the body and was known in Gaelic as the feileadh mor meaning large and folded, or pleated. It was normally made up of two pieces of material...
The page says it is a quote from the Scottish Tartans Society, which seems to be defunct.

Any thoughts on this?