The fourth blessing- Hatov V'hameytiv- is d'Rabban (added by the Rabbis). As stated on 48b: "Hatov V'hameytiv B'Yavneh tiknuha k'neged Harugai Beitar". (The blessing 'Hatov V'hameytiv' was appointed by the Rabbinic leaders in the great Yeshiva in Yavneh because of the Miracle done for the Martyrs of Beitar.)
The Gemara continues that the double expression [Hatov V'Hameytiv] of G-d's goodness is because:
1. The Romans slaughtered the population of Beitar. Thousands of corpses did not
rot even after several years of exposure to the elements.
2. The Romans finally relented and allowed the martyrs to be given proper burial.
One could justify continuing their study of this page and leave the Beitar story behind while thinking "I got the point- next!" After all, the crux of Perek Sh'vi'i (chapter 7) of Berachos is Birchas Hamazon- not Beitar.
The wise Talmudic student examines all the marginal notes on the folio. To get a fuller appreciation of the Beitar story and its historical perspective, let's take a look at a couple:
The picture above is a scan of a portion of Berachos 48b. Notice on the right margin the area framed in red. This section is titled RAV NISSIM GAON. (His last name isn't Gaon, but a recognition of respect for his wealth of knowledge and ability to lead and teach others).
Rav Nissim lived close to the end of the Geonic period, dying in 1050ce. He was a student of Rav Hai Gaon, possibly the most famous of the Geonim. Rav Nissim is classified as an early Rishon. (Rashi, the most widely read of the Rishonim, was born in 1040ce.)
Rav Nissim's marginal comments are scattered throughout Berachos wherever he sees the need to elaborate on the discussion in the Gemara. Most often it is to point out the source of brief references in the text. With regard to Beitar, he evokes the famous last Mishna in Maseches Ta'anis, page 26b, where the Rabbis indicate that the greatest day of joy in the Jewish calendar is the 15th of Av, just a few short days after the belaboring 25 hour fast on the 9th of Av, when we sadly commemerate the day the Holy Temple fell twice in history!
The ensuing discussion in the Ta'anis culminating on page 31a relates that the 15th of Av is the day the Romans finally relented in allowing the Beitar martyrs to be buried (see above).
Continuing in his comments on Berachos 48b, Rav Nissim Gaon also points out the narrative in Gittin 57a that deals with a series of incidents in Jewish History when a population is collectively punished for acting impulsively. Here, the point is made that Beitar is one such occurence.
Those piqued by curiosity will open up Gittin (the tractact that deals primarily in divorce and other matrimonial issues) and learn that the Romans punished Beitar for killing a convoy of Roman soldiers who chopped down a tree grown specifically to be used as a wedding canopy. The soldiers needed it to replace a broken wheel on a wagon used by the daughter of the Roman governor.
Beitar was also the seat of rebellious authority led by Bar Kochba and the famous Tanna Rabbi Akiva. According to a statement made on Gittin 57a, Beitar was a kilometer off the Mediterranean coast. This does not necessarily conform to the opinion of others who claim it is near modern day Beitar Illit, a southwestern suburb of Jerusalem.
As this was the final straw in the irritations suffered by an undersized (for the job) Roman Legion, it was too easy for the Romans to sail over quickly with a superior battalion of Legionaires and pour their wrath on the entire local citizenry of Beitar.
Thus, the great Rav Nissim Gaon of the early generation of Rishonim reminds us to not just read the immediate text in the Gemara, but to investigate and learn the entire history of the Beitar storyline.
Also notice (in the picture above) the left margin with blue lines near text. This area marks a reference from the Mesoras Ha'shas to look at Bava Basra 121b to follow another perspective on Beitar.
Bava Basra deals with tort law, specifically with issues relating to partnerships, exchange of merchandise as well as some laws of inheritance. The connection to Beitar is indirect in that the miracle of the Beitar burials is one of a few reasons we celebrate the 15th of Av as a day of joy. Another reason (outlined in Ta'anis 31a) is that it is the day that the tribe of Benjamin is once again allowed to intermarry with the other tribes. The chapter that discusses the joy of 15 Av is enveloped by other points of order:
Who is allowed to testify for a group of people, i.e. a tribe? There are 12 tribes broken up into 13 areas of land distribution in biblical times. There is a point during the Judges time period, not long after Joshua is no longer around, where there is infighting among the tribes. Subsequent restrictions are placed against allowing fraternization. Not only are there issues of property rights inter-tribal, but also societal relationships.
The universal acceptance of the 15th of AV as a holiday puts an end to the internecine fighting as well as the injustice perpetrated to the martyrs of Beitar.