This study identifies and analyses the legal rules followed in Vindolanda, a Roman military settlement erected in the first century AD to separate the Roman province of Britannia from the unconquered Caledonia. In particular, the focus is on the rules followed by military officers of different ranks stationed therein and the legal powers held by them. This subject has scarcely been explored by Roman law scholars due both to the paucity of Roman legal sources on this point and the traditional conception of Roman military law as of secondary relevance in comparison with Roman private law (although, recently, this opinion has been changing). In addition, such an investigation aims to shed light on the processes of integration and Romanisation put in place in Vindolanda, where soldiers of different origins lived together. For this purpose, the study considers the Vindolanda tablets, a conspicuous corpus of messages written by the inhabitants of Vindolanda. These tablets, unearthed by archaeologists and whose text has been restored by philologists, palaeographers, and papyrologists, are firstly examined from the legal perspective, to identify the legal rules implied or, sometimes, explicitly enunciated by them. Subsequently, these legal norms are considered collectively, to grasp some common tendencies and, consequently, appreciate the legal integration between different people in Vindolanda. Eventually, these legal rules are compared with Roman legal rules, to verify to what extent they adhered to the ‘Roman model’. It is possible to conclude that in Vindolanda some Roman legal rules were applied without exceptions, such as the use of the Latin, the official language of the Empire; the prohibition on withdrawing an accusation; and the principle of collegiality in establishing a penalty. Not unexpectedly, in Vindolanda, that is, a Roman military settlement far from Rome, and, consequently, less subject to control, other Roman principles were adapted to its specific reality. For instance, the praefect granted leave, in spite of the Roman legal rules that thwarted this practice, and the presence of women is well attested, notwithstanding the prohibition on them to stay in military camps. What emerges is a climate of trust and collaboration, determined by the adherence to common rules, partly corresponding to Roman law.