I am able to handle BCE dates in the following way:
dataTable.addRows([
['Socrates', new Date(-470,0,1), new Date(-399,0,1)],
['Plato', new Date(-428,0,1), new Date(-348,0,1)],
['Aristotle', new Date(-384,0,1), new Date(-322,0,1)],
['Euclid', new Date(-325,0,1), new Date(-270,0,1)]
])
However, I get errors when I attempt to add a row that spans the BCE/CE divide.