>I am researching the practice of rundale (runrig in Scotland) in land
>distribution/allotment. What is the earliest known date for this

Francine, a chara,

My first thought was to check the DIL for entries, then I realized I didn't
know the word for "rundale" in Irish.  The standard English-Irish and
English-Gaelic dictionaries don't have it, so I turned to the Stòrdàta
Briathrachais Gàidhlig at Sabhal Mór Ostaig
( and came up with "fearann-tuatha"
and "roinn-ruithe" in Scottish Gaelic.  Working back from "roinn"
(= division) in O Dónaill's Irish dictionary I came up with "roinn iomairí"
(lit., division of (ploughed) ridges), which is translated as "rundale" -

Now, back to the DIL to check under the OI spelling "immaire", translated
as "ridge, furrow", where it says "immaire" was "often used as a division
or measurement of land or distance".  None of the citations directly refers
to the practice of rundale. This one, however, from "Bethu Phádraic"
(written in the 9th cent.), is interesting:

"dorónai oifrend for cech sechtmad immbairiu do neoch imrulaid i

= you make an offering of every seventh "immaire" to one who [?] in Munster

I'm not sure of the verb here ("went away"??) and don't have time to track
it down, too, but the line points to the division of agricultural land into
"ridges" or long strips at an early period.

It's also worth noting that Irish does not appear to have a single unitary
technical term for the practice, but rather a descriptive phrase.

I hope this is useful!