Probably an olive or acacia, as far as scholars can determine.
Of course there are scholars who have poked into the matter.
The Roman Empire sensibly used the most accessible wood.
Me personally I would bet on the acacia which grows bigger
And broader and quicker than olive. You wonder if someone
Grew them for just this use. A market niche with an imperial
Budget, who could argue with that as a business model? Not
To mention the excellent public relations aspects of assisting
The mills of justice, the civic equilibrium, the battles against
Criminals and radicals. Imagine it: an acacia grows in Judea,
Letís say in Ashkelon, near the sea. It is harvested at twenty,
Planed with its brothers, and trundled to Jerusalem. The load
Is stamped and recorded, bills of sale and receipts are issued,
A few of the timbers are mysteriously lost in transit and filed
As cost of business, and one ends up on Golgothaóthe Skull.
Poor creature, remembered only for its last burden. But recall
The birds it housed, the birds it sensed whizzing pastóderor,
The swallows and swifts, the small gleaming knives in flight,
And selah, the quail in their vast flocks, carpeting the acacias
In October like feathery jackets, and anafas, the patient heron,
And hasidah the stork and larus the gull and nesher the eagle,
And certainly yonah, the dove. Imagine our acacia held seven
Dove nests in its twenty years. Imagine the gentle burbling of
Chicks is the last music it remembered as the axe bit. Imagine
It never knew or imagined the gaunt being it held at the finish.
Poor thing, remembered for what it never knew it was bent to;
But celebrated quietly this morning, as another young life lost.