Shabbat boundary rock w... JPost - Arts & Culture - Entertainment
I don't normally get around to reading the "Jerusalem Post," but it stands to reason that it would have some good articles about recent archaeological discoveries in the region.
You can't "work" on the Sabbath, right? And travel constitutes work. But how far can you walk before it's "travel"? Well, of course, there's a rule for that. And in the city of Jerusalem, there were markers that denoted the limits of Sabbath walking-around-which-is-not-technically-travel.
The discovery consists of a rock with the word "Shabbat" inscribed in Hebrew; the best date is between 1st and 7th centuries CE. Not too precise, but perhaps further discoveries of similar stones will narrow it down.