Tony Honoré summarizes Caracalla's legal activity as follows: "Certainly his rescripts are not open to the criticisms directed against them in the Historia Augusta. His reign is marked by a good flow of legal opinions of high quality. At most one might object that some texts of 212-13 tend to grant indulgences to soldiers contrary to strict law. But this is itself evidence of the personal attention given by Caracalla to the relevant petitions".
An overview of known instances of Imperial adjudication can be found in: K. Tuori, The Emperor of Law: The Emergence of Roman Imperial Adjudication, Oxford 2016, 384-416.
An overview of constitutions in the Codex Iustinianus can be found in: B.W. Frier, Codex Iustinianus. A New Annotated Translation, with Parallel Latin and Greek Text. Based On A Translation By Justice Fred H. Blume, Cambridge 2016, volume 1, 3094-3099 (with the comment for those sine conss.: In iis constitutionibus, a quibus tituli incipiunt, haud raro dubium est, utrum Caracallae an Pio vel Marco vel etiam Elagabalo tribuendae sint).
An overview of other legal texts can be found in: G.F. Haenel, Corpus legum ab imperatoribus romanis ante justinianum latarum, quae extra constitutionum codices supersunt, Leipzig 1857, 152-156.
An overview of rescripts in the Codex Justinianus linked to Rome can be found in: T. Honoré, Emperors and Lawyers, London 1981, 29. Note the assumption "Caracalla on German campaign".
'Caracalla' by Sir Lawrence Alma-Tadema (1902).
Image: Wikimedia.