The 1889 treatise * Arithmetices principia, nova methodo exposita* (

The treatise is written in
Latin, which was already somewhat unusual at the time of publication, Latin having fallen out of favour as the
lingua franca of scholarly communications by the end of the 19th century. The use of Latin in spite of this reflected Peano's belief in the universal importance of the work – which is now generally regarded as his most important contribution to arithmetic – and in that of universal communication. Peano would publish later works both in Latin and in his own artificial language,
Latino sine flexione, which is a grammatically simplified version of Latin^{[
citation needed]}.

Peano also continued to publish mathematical notations in a series from 1895 to 1908 collectively known as Formulario mathematico.

**^**Segre, Michael (1 January 1994). "Peano's Axioms in their Historical Context".*Archive for History of Exact Sciences*.**48**(3/4): 201–342. doi: 10.1007/bf00375085. S2CID 122070745.**^**Clegg, Brian (7 February 2013).*A Brief History of Infinity: The Quest to Think the Unthinkable*. Little, Brown Book Group. ISBN 9781472107640.

- English translation (with original Latin): https://github.com/mdnahas/Peano_Book/blob/master/Peano.pdf
- Original treatise (in Latin, scanned) at Internet Archive: https://archive.org/details/arithmeticespri00peangoog