It is a mistake to consider the Romagna territories as part of the Old Italian States: it is in fact, as we'll see, a territory where special stamps were put in use for special reasons.

The 2nd Independence War saw several changes in the territory and in the Italian political arrangements and ended with the unification of a large part of the territory under the Vittorio Emanuele II flags.
The first territories of the Roman States that went in Sardinia hands were, in fact, the Romagne ones that comprehended the provinces of Ferrara, Bologna, Ravenna and Forlì, Papal territory since 1503.
The Magenta defeat (June 4th 1859) inflicted by Sardinia and France, determined the retreat of the Austrian troops and the abandonment of the Romagne territories to start with the troops of the general Habermann based in Bologna (June 12th 1859) to finish with Rimini (June 22nd 1859). The Roman States troops too cannot contain the Sardinian troop advance, reinforced by the recent popular insurrection movements. June 15th 1859 a Provisional Government was set; it was definitively placed under the leadership of Lionello Ciprani, who substituted the "Regio Commissario" Massimo D'Azeglio. In September 7th the Roman State dominion was officially declared finished. Between the November end and the beginning of December 1859 together with the ex-Duchies territories of Modena and Parma, the Romagne were placed under the Farini dictatorship (who becomes "Governor" from January 1st 1860) with the name of "Regie Provincie dell'Emilia".
The territories were definitively annexed to the Sardinia kingdom March 15th 1860.
It would be a mistake to think that everything went so fast without any problem. The real historic-political situation of that period was, to say the least, tangled, and even the historical dates differ quite a lot from one source to another! Events with different outcomes and, as we would say today, "political push and pull" between Piedmont, Austria, France and Roman State made the social-political situation really "Machiavellian" type: it's enough to think, for instance, to the Sardinia decision (Villafranca Armistice) of not taking anymore interest to those territories, on the contrary to give them back to the Pope! (at least in theory...). The results was the formation of a defensive League between Ricasoli (in Firenze), Cipriani (in Bologna) and Farini for Modena & Parma, with the aim to protect themselves to the possible return of the old regimes. After various events, as said, was Farini who with strong authority, brought the territories to the definitive annexation. I will not deal here with the events that followed because they would bring us to an excessive historic content. To the people who wants to study in details this interesting period, I suggest to consult the "Bibliography" section where several books really complete on the subject are listed.

The initial circulating currency was the Roman State Scudo, divided in 100 Bajocchi. One Scudo was worth 5.375 Lire and one Bajocco was equivalent to 5 centesimi. From June 28th 1859 by a decreee the Italian Lira of 100m centesimi was introduced. It will officially enter in circulation November 1st, by setting one Scudo to 5 Lire and one Bajocco to 5 centesimi. The Mezzo Bajocco was supposed to be equated to 3 centesimi (thing that, as we'll se, did not happen).

Also the rates for postage reflect the period very confuse. At the beginning the pontifical stamps continued to be used. Very soon they became insufficient also for the Roman State use to provide small quantities of stamps. This fact brought to the creation of split parts to make up for the lack of missing values.
When the available stamps ended (July-August 1859) the solution was to mark on the letters the tax due with a cancellation (1/2, 1, 2, 5) or by hand and paying the corresponding amount by cash at the Postal Office (Fig. 1).

Fig. 1:
the notice of June 16th 1859

From September 1st the Romagne stamps became available (see the issue introduction) that remain in use officially up to January 31st 1860 but were tolerated also in the following month because the Sardinian ones in use from February 1st, have been distributed in quantities totally insufficient...

Here are the main postal rates for a letter first carriage for the interior (one sheet letter). The double carriage paid double, the triple paid triple etc.. At the beginning until January 31st 1860, the pontifical rates continued to be used and precisely:

Inside the same Postal District
1 bajocco
Between neighboring Postal Districts (and on the same Postal path)
2 bajocchi
Between Postal District not neighboring but at the same "distance"
3 bajocchi
The same if at different "distances"
4 bajocchi
One sheet printed material (whatever location)
1/2 bajocco
Printed material (more than one sheet, up to one ounce of weight)
1 bajocco
Printed material (for each additional ounce)
1 bajocco
Certified mail

From June 20 1859 the cost of a letter was calculated by weight (10 grams each carriage) and not anymore by sheets (with the exception of the military mail that paid 1 bajocco always) and from November 1859 the Italian Lira was introduced with the following adjustment (to be noticed that differently from what stated by Italian Lira introduction decree of June 28th 1859, the new October 27th 1859 decree equated the Mezzo Bajocco to 2 centesimi instead of 3: this fact created confusion to the point that in some offices the equivalence was made at 2 centesimi and in others at 3 centesimi!):

In the same Postal Office
5 centesimi
1 bajocco
Inside 20 Km
10 centesimi
2 bajocchi
More than 20 Km
20 centesimi
4 bajocchi
Periodic printed material (each 40 grams)
1 centesimo
1/4 di bajocco
Not periodic printed material (each 40 grams)
2 centesimi
1/2 bajocco
Certified mail
25 centesimi
5 bajocchi
Military mail