Reference edition:

A. Grillone, Gromatica militare: lo ps. Igino. Prefazione, testo, traduzione e commento, Bruxelles 2012 (Collection Latomus 339).

A manuscript of the 6^th c. (A) provides our only copy of Ps. Hyginus’ De metatione castrorum, a short treatise of 58 chapters on military science.  The first chapters provide information about the quarters normally assigned to the legionary cohorts and vexillarii (§1-5 ) and deal with the area on either side of the praetor’s tent (§6-13); §14-16 describe the praetentura and §17-19 treat the retentura and the foreigners’ areas; §20-1 deal with the via sagularis running around the camp and the blueprints for different camp arrangements; §22 explains where each division should be placed; §23-4 briefly offer zone-by-zone blueprints for the latera praetorii and the praetentura, while §25-9 do so more expansively for the retentura.  Apart from the supplementary information in the section on foreign troops, which includes a description of camel battalions, Ps. Hyginus offers certain clarifications on the cohortes peditatae and explains the calculation for the cohortes equitatae: although this is more complex in that it consists of both foot and horse, it is simplified through a ratio that treats horse as if they were foot.  After a list of the different divisions (§30), the author presents a “new system” of metatio that is recommended for an army of three legions flanked by auxiliary units identified by the author (§31-44).  It seems reasonable to infer that the “new method” advertised in §45-7 consists of a symmetrical arrangement of the cohorts within an army of three legions.  The last part of the work (§48-58) briefly surveys the camp’s various defenses (fossa, titulum, vallum, lorica, cervoli, armorum ordines, agger, coxae, claviculae), ending with a description of how to select campsites, the ascensus valli, and tormenta.  It must be emphasized that the work lacks the initial part, as evidenced by an incipit (nunc papilionum tensionem cohortium supra scriptarum) that refers to previous informations on legionary cohorts; moreover, given that the last lines of the text offer new information without any conclusion akin to the sign-posting one finds at the end of the first and second parts (i.e. §22 and §45-47), some scholars have suggested that we are also missing a conclusion to the third section and to the entire treatise (Gemoll, Lenoir, contra Grillone).

The most famous title for this work, the Liber de munitionibus castrorum, derives from the humanistic period (though it was deemed authorial by Lange 1848); however, since the aim indicated by the work’s main argument is not munitio (i.e. fortifications), but rather metatio (i.e. camp measurements), Grillone prefers to accept the title proposed by Pontano: De metatione castrorum liber.

Very little in the work allows us to arrive at a firm dating.  However Grillone thinks that fair estimates of termini post and ante quem may be based on the following evidence: in the former case, one may note Ps. Hyginus’ description of legionary cohorts being ordered by century - a development that can most likely be dated to the reign of Hadrian; in the latter case, the crucial passage is the author’s insistence that the army includes a legatus legionum, a post attested for the last time in an epigraph dating to between 253 and 259 AD.  Concerning the terminus ante quem, however, Grillone also considers two other references: first, to the legionary cavalry, which allows us to date the text to before 242 AD, the last year in which we find epigraphic evidence for this unit (these are probably at least in part the equites mentioned in §52, et equites alterna vice castra circuire debent, since the term is not accompanied by any qualifiers, as is generally done when indicating units of the auxiliary cavalry; cf. Veg. mil. 3.8.19); second, to certain legions as provinciales, an adjective that suggests the treatise was written before Caracalla’s citizenship edict of 212 AD.  Conversely, to push the terminus post quem to a later period, one might rely on the use of works like papilio, praetentura, and retentura: at least in surviving evidence, these are all used at a late date that suggests the start of the 3^rd c.  [B. Strona; tr. C. L. Caterine].