Traditionally, the weeks between Pesah and Shavuot – the days of Sefirat HaOmer – are kept as days of mourning. The likely source for this tradition appears on our daf, where the Gemara quotes Rabbi Akiva as teaching that even a person who studied Torah in his youth should continue to study Torah into his old age. Similarly, someone who teaches students as a young man should continue to do so even when he gets old.
To illustrate the importance of this teaching, the Gemara relates that this concept was crucial for Rabbi Akiva personally. Rabbi Akiva is said to have had 12,000 pairs of students across the land of Israel, and all of them died during the period between Pesah and Shavuot. The land was left desolate until Rabbi Akiva taught a new group of students – Rabbi Meir, Rabbi Yehuda, Rabbi Yose, Rabbi Shimon and Rabbi Elazar ben Shamua – who succeeded in reestablishing Torah study in Israel.
The simple reading of the Gemara makes it appear that Rabbi Akiva’s students died of a plague, and most of the rishonim accept that approach. In his historical letter, Rav Sherira Gaon offers a different explanation. He says that they died of shemada, which means a war or governmental decree. This is an apparent reference to the Bar Kokhba revolt, of which Rabbi Akiva was an enthusiastic supporter. It appears that Rabbi Akiva’s students volunteered for military service under Bar Kokhba’s leadership, and when the revolt was put down by the Romans with great severity, they were among the many who were killed. The Meiri suggests that the source for the tradition of mourning during this period stems from this story. According to the ge’onim the students did not die on the 33rd day of Sefirat HaOmer, which is why there is no mourning on that day.