All Intensive Purposes

At Marginal Revolution, Alex Tabarrok posts part of a 1796 treaty between the fledgling United States of America and the Bey of Tripoli:

As the government of the United States of America is not in any sense founded on the Christian Religion; as it has in itself no character of enmity against the laws, religion or tranquility of Musselmen; and as the said States never have entered into any war or act of hostility against any Mehomitan nation, it is declared by the parties that no pretext arising from religious opinions shall ever produce an interruption of the harmony existing between the two countries.

Seems relevant to an originalist interpretation of the Establishment Clause.