On today’s daf the Gemara discusses a rabbinic ordinance established by Yosei ben Yo’ezer of Tzereida and Yosei ben Yoḥanan of Jerusalem who decreed impurity upon the land of the nations. The Sages decreed that anything – person or vessel – that comes in contact with or carries that soil becomes impure for seven days, like the impurity of one who comes into contact with a corpse.
The impurity of the land of the nations is already alluded to in the Prophets: “On impure land you will die” (Amos 7:17). However, in the Mishna, this impurity is listed as one of the cases of uncertain impurity due to the concern that a dead person may be buried there. Since graves were not always marked and since cemeteries for burial were not clearly set aside everywhere, there was concern that any clod of dirt could be from a decaying corpse or could have come in contact with the flesh of a corpse.
The question raised in the Gemara is that it appears that this decree was established not by Yosei ben Yo’ezer of Tzereida and Yosei ben Yoḥanan of Jerusalem, but by other groups of Sages. Specifically, the Gemara suggests that this is recorded as one of the ordinances of Usha. Ultimately, the Gemara explains that there were different stages so that over time the decree expanded to include not only the soil but the air as well.
The town of Usha in the Galilee was, for a time, the seat of the Sanhedrin. Many ordinances were instituted there relating to various areas of halakha, including halakhot of ritual purity and impurity and monetary laws. The Sages disagreed with regard to the exact date of the Usha regulations, since the Sanhedrin’s stay there was interrupted. Nevertheless, apparently these ordinances were instituted after the failure of the Bar Kokhba rebellion, approximately seventy years after the destruction of the Temple.
According to Rosh HaShanah (31a), during the period of the destruction of the second Temple God began to withdraw His Divine Presence from the Temple. In parallel, the Sanhedrin removed itself as well, first within the city of Jerusalem, and ultimately to the Galilee. It was first transplanted to Yavne, from there to Usha, Shefaram, Beit She’arim, Tzippori, and Tiberias.