Foundational texts for Rosicrucianism include:
The Fama Fraternitatis (c1614) (123KB PDF)
The Confessio Fraternitatis (c1615) (93KB PDF)
The Consideratio Brevis of Philip a Gabella (c1615) (159KB PDF)
The Chymical Wedding of Christian Rosenkreutz (c1616) (4525KB PDF)
The Ara Foederis Theraphici (c1617) (84KB PDF)
The Pandora of the Sixth Age (c1617) (984KB PDF)
The Mirror of the Wisdom of the Rosy Cross (c1618) (631KB PDF)
A catalogue of these and many other Rosicrucian texts was compiled by Frederick Leigh Gardner and privately printed in 1923 (2nd edn) (10.5MB PDF).
"A Letter from the Brotherhood of the Rosie Cross concerning the invisible magical mountain and the treasure concealed therein", translated by Kenneth R.H. Mackenzie and published in the Rosicrucian and Masonic Record (vol.1, No.3 15th March 1875) offers further insight (467KB PDF).
The "Themis Aurea - Laws of the Fraternity of the Rosie Crosse", by Michael Meier (English trans. c1656 dedicated to Elias Ashmole) (8.5MB PDF) might also be of interest, as might the lengthy entitled anonymous text, "An Open letter or uncomplicated answer to the highly enlightened Fraternity of the highly laudable Order of the Rose Cross to its published Fama and Confessio of the Fraternity" (c1615) translated by Ruud Muschter in 2012, and the c1618 poem, "Altar of the Theraphic Brotherhood Fraternitatis Crucis Rosae", by John Knuber (translated from the German and found in the papers of FF Schnitger) (473KB PDF).
Another text which possibly influenced the founders of the SRIA was the "Geheime Figuren der Rosenkreuzer aus dem 16en und 17en Jahrhundert" (c1785), which related to the earlier German 'Order of the Golden and Rosy Cross' (c1750). Note: The linked PDF copy (48.2MB) was procured from the Archive.org website. Free PDF copies of this text, translated into English, have been procured from the AMORC website, in three sections: Preface (1MB), Book 1 (8MB), and Book 2 (6.6MB). From the Geheim Figuren we also have the Rosicrucian Prayer (2MB PDF).
Aside from the detailed "History of the SRIA" (2003), by TM Greensill, copy of which is provided to our members, the following might also be of general interest on the roots of the SRIA:
"Lives and Doctrines of Great Master Builders - Christian Rosencreutz" (1.4MB PDF)
Dr William Wynn Westcott's "Rosicrucian Thoughts on the Ever-Burning Lamps" (94KB PDF)
Thomas de Quincy's (c1824) "Historico-Critical Inquiry into the Origin of the Rosicrucians and the Free-Masons" (7.7MB PDF)
Dr William Wynn Westcott's (c1915) survey of the first 50 years of "The Rosicrucian Society of England" (507KB PDF)