1866 - 4 baj bright yellow, left sheet-margin canc

 1866 - 4 baj bright yellow, left sheet-margin canceled with Papal grid postmark, in mixed franking with Kingdom of Italy 20c on 15c 'horseshoe' 1st type, cancelled 'FIRENZE 20 SEP 66', on cover from 'ROMA 19 SEP 66' to Florence. Franking pays double rate for Papal tariff and single rate for Italian tariff. Extremely rare; signed Sorani, Oliva; certs. Bottacchi and Diena: 'only three such mixed frankings recorded'. (Sassone 5Aa + Italy 23 - Euro 180,000++)