Button Help Please and Thank You.

[fyrffytr1]

I found this button yesterday at a mid 1800s site. I couldn't tell what it was until I cleaned it using electrolysis. I think I remember seeing something like this before. At first I thought it was a house on a hill but a friend suggested that it may be a fort instead.
The back was full of crud but I think there is loop visible now. It may have been iron or tin backed.