Per acconciar bene una porchetta (how to roast a pig) in Maestro Martino da Como, De arte coquinaria 1456 (Washington, Library of Congress, Medieval Manuscript n. 153):

After opening the pig, removing the viscera and washing it carefully, turn it so the rind stays inside, then stuff it with a mixture of its liver, aromatic herbs (parsley, marjoram), garlic, lard, cheese, eggs, pepper and saffron.

Roast it on the spit, brushing it with a brine enriched by vinegar, pepper, saffron, laurel or sage or rosemary.

De porcellanis assatis idest de porchettis in Libro cuquinaria bonarum c. 63v. (Châlons-en-Champagne, Bibliothèque Municipale Georges Pompidou, 319 ms. Copied in 1481):

Stuff the pork with garlic, fennel, salt and spices.

Roast it on the spit then serve it with a cooked sauce made with its liver mashed with marjoram, spices and saffron diluted with vinegar and cooked must.

The filling of this recipe is the one that most resembles the preparation of porchetta in central Italy and in particular in Umbria.

Belted black swine,  particular from the Church of Santa Maria a Vallo di Nera (Pg), 1383