Background and historical information
C. Sallustius Crispus, as a reward for his service to Julius Caesar in the civil wars in the early 40s B.C., was governor of the new province of Africa Nova in 45 B.C. (see “Sallust”). This province corresponded more or less to the old kingdom of Numidia. Sallust thus gained personal experience of the territory in which the Jugurthine War had taken place six decades earlier. He allegedly even perused books in the library of the Numidian kings (17,7).
In retirement after 44 B.C. Sallust wrote the Jugurthine War before turning to his most ambitious work, the Historiae (see “Sallust”, C.2.c). Because both works are thematically connected, he probably had the latter …
Parker, Victor. "Bellum Jugurthinum". The Literary Encyclopedia. First published 23 September 2013
[https://www.litencyc.com/php/sworks.php?rec=true&UID=35059, accessed 20 February 2019.]