Meagan Ayer, ed. (2014) [1903]. "Variable Nouns §107". Allen and Greenough's New Latin Grammar for Schools and Colleges. Boston: Ginn & Company. p. 44. ISBN978-1-947822-04-7. Retrieved 14 October 2021 – via Dickinson College Commentaries, Department of Classical Studies, Dickinson College, Carlisle, PA.
Richardson 2001, pp. 171–185. Richardson, Alan (2001). "The order of battle in the Roman army: Evidence from marching camps". Oxford Journal of Archaeology. 20 (2). doi:10.1111/1468-0092.00129.
Richardson 2002, pp. 93–107. Richardson, Alan (2002). "Camps and forts of units and formations of the Roman army". Oxford Journal of Archaeology. 21 (1). doi:10.1111/1468-0092.00151.
Lewis, Charlton T.; Short, Charles (1879). "castrum". A Latin Dictionary. Retrieved 1 July 2025 – via perseus.tufts.edu. The plural form, castra, had a possible meaning of "tents".