Ex qua die arcano is the incipit of the 4 March 1853 apostolic letter by which Pope Pius IX decreed the reestablishment of the episcopal hierarchy in the Netherlands. Through it, the administrative area formerly known as the Dutch Mission was divided into dioceses. Utrecht was raised, once more, to a Roman Catholic archdiocese, and received the four suffragan dioceses of Haarlem, 's-Hertogenbosch, Breda, and Roermond.
- Pope Pius IX (1853-03-04). Martinis, Raffaele de (ed.). "Ex qua die arcano". Iuris pontificii de propaganda fide: pars prima, complectens bullas, brevia acta S.S. a congregationis institutione ad praesens iuxta temporis seriem disposita (in Latin). Romae: Ex Typographia Polyglotta (published 1894). 6 (1): 158–161. OCLC 3342505. Translated in One or more of the preceding sentences incorporates text from this source, which is in the public domain: "XIIIb: the apostolic letters of the most holy Lord Pius IX, by Divine Providence, pope, by which letters the episcopal hierarchy was re-established in Holland". Further papers regarding the relation of foreign states with the Court of Rome: presented to the House of Commons by command of Her Majesty, in pursuance of their address of June 14, 1853. London: Harrison and Son. 1853. pp. 61–65. OCLC 80498785.