Fidelitas in the Kingdom of Hungary, Transylvania and the Holy See, 1100-1400: feudal loyalty, the nota infidelitatis, and the constitutional bond

Fidelitas — the feudal and constitutional obligation of faithfulness owed by the noble to the king — is the foundational bond of medieval Hungarian public law. This study traces the term across 5,547 Hungarian records (Árpád period, 1100–1301: 2,218 of 11,148 charters, 19.9%; Angevin period, 1302–1400: 3,329 of 33,882, 9.8%), 1,250 Transylvanian records (12.5% of 9,986), and 376 papal letters on Hungary (6.5% of 5,787). The 19.9% Árpád rate is the highest of any concept studied in this series. Four functional categories structure the analysis: grant citations (ob/pro fidelitatem, 349 HU records), the nota infidelitatis and forfeiture proceedings (326 HU records), the oath of fealty (296 HU records), and the fidelis noster address formula (735 HU records). The oath-pledge category triples from the Árpád to the Angevin period (59 to 237 records), recording Charles I's systematic constitutional reinvestiture of the barons. This study is a corpus study: it counts and reads what a large body of edited medieval documents says about one concept, and sets that against modern scholarship. It was prepared with software and AI assistance. The counts, tables, charts and first draft were generated by a program (publisher.py) from the author's corpus, without a language model. The search rules, the concept's introductory paragraphs and the interpretive paragraphs were written with the help of an AI system (Claude, Anthropic), and a random sample of the matches was read in full to measure how many are true instances (section 2). The author read and approved the text before publication. Readings of the Latin marked as preliminary have not yet had a specialist's close reading. The counts depend on what the editions print and how their editors summarised it: editions are uneven by region and decade, modern summaries carry their editors' interpretations, and OCR may miss or misread words, so the numbers show proportions and trends, not totals. The study has not been peer reviewed. Corrections are welcome and will be published as new versions of this record.