One of the most significant groups of documents in the Siret Archive comprises his manuscripts and a vast quantity of written material in the form of notes, texts, dossiers and studies, mostly on archaeology. Almost all of them found their way into publications, although a few were never publicly released and for this very reason are especially fascinating.
The collection includes some of his greatest works, seminal compilations such as L'Espagne Préhistorique, Listes Générales des Sépultures, and Analyses.
In two albums of illustrated plates and one volume of text from L'Espagne Préhistorique, Siret documented the most important archaeological sites of prehistoric Spain, drawing on both scholarly literature and his own research and accompanying the data with plates of grave goods and structures. In his Listes Générales des Sépultures, he used a grid to cross-reference data on Neolithic, Chalcolithic and Early and Middle Bronze Age sites, as well as the ones excavated by Siret which he dated to the Iron Age. In Analyses he presented the results of numerous metal analyses, focusing particularly on the silver content of samples taken from different houses at Almizaraque and on the copper alloys of metal objects in his collection.
If there is one thing that characterised Louis Siret's archive, it was that he never stopped using it; documents would be moved from one folder to another depending on his interests at any given time, making them harder to classify and place in order after the fact. This is true of his dossiers, which contain bibliographic notes, drawings, sketches, comparisons of pieces and sites, texts, etc. that Siret used as reference material when writing articles such as "Orientaux et occidentaux en Espagne aux temps préhistoriques" (1907), "Religions néolithiques de l´Ibérie" (1908) and "Questions de chronologie et d’ethnographie ibériques" (1913).