The database Ut per litteras apostolicas ... Papal Letters (LITPA) represents an electronic version of the celebrated Registres et lettres des Papes du XIIIe siècle (32 vols.: Rome, 1883- ) and the Registres et lettres des Papes du XIVe siècle (48 vols.: Rome, 1899- ). Furthermore, it has been enriched with unpublished material (litterae communes of Gregory XI from 1371 to 1375 and the registers of petitions of Urbain V).
Ut per litteras apostolicas provides striking information on the most varied aspects of medieval society: church institutions, the clergy, the papal states, politics, the legal system, taxation, government and finance, secular society, the religious life, intellectual and artistic life, the economy, wars, law and order, the environment and natural disasters, and daily life.