Here the Prussians showed themselves extremely politic and reasonable.
Realizing that, with the advance of artillery, the great rock-fortress
no longer had the military value of earlier days, they not only raised
no objections to the evacuation of Luxemburg by their troops, but in the
Congress it was they who proposed that the territory of the Grand Duchy
should be neutralized 'under the collective guarantee of the Powers'.[6]
A treaty was therefore drawn up on May 11, 1867, of which the second
article ran as follows:--

'The Grand Duchy of Luxemburg, within the Limits determined by the
Act annexed to the Treaties of the 19th April, 1839, under the
Guarantee of the Courts of Great Britain, Austria, France, Prussia,
and Russia, shall henceforth form a perpetually Neutral State.

'It shall be bound to observe the same Neutrality towards all other
States.

'The High Contracting Parties engage to respect the principle of
Neutrality stipulated by the present Article.

'That principle is and remains placed under the sanction of the
collective Guarantee of the Powers signing as Parties to the present
Treaty, with the exception of Belgium, which is itself a Neutral
State'.[7]

The third article provided for the demolition of the fortifications of
Luxemburg and its conversion into an open town, the fourth for its
evacuation by the Prussian garrison, and the fifth forbade the
restoration of the fortifications.