Unst - walled enclosures without doors?

[chall]

I was staying on Unst last week, and went walking around the cliffs east of Clibberswick in the north east part of the island. In the fields around the south side of the peninsula (ie the north shore of Haroldswick) I noticed a series of walled enclosures, such as in the attached picture.

The walled enclosures were mostly square, although some were more circular. The square enclosures had sides of around 4-5m in length, and around 1.5m in height.

The exceptionally curious thing, is that none of them had doors, windows, or other obvious ways of entry / exit. I therefore wonder what on earth they were for, and wondered if anybody might know.

Many thanks.

Chris

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[aitch]

Hello Chall.
If you had posted this question a couple of years or so you would have snowed under with an avalanche of replies, sadly since then this forum has dramatically decreased in postings.
I am not, again I use the word "sadly" a Shetlander but have visited these fabulous islands on a couple of occasions and I believe they were formerly used for the cultivation of crops and the walls were meant to keep out the sheep.
I may be wrong but hopefully if I am someone with more knowledge than I can shed a light on your query.