We read in Parashat Bamidbar of the census taken by Benei Yisrael after the construction of the Mishkan, which found that they numbered 603,550 adult males. This figure forms the basis of the well-known view among the Rishonim that the prohibition against carrying in a public domain on Shabbat applies only in public areas with 600,000 people. The Gemara in Masekhet Shabbat (98a) establishes that the Israelite camp in the wilderness (“diglei midbar”) forms the paradigm of a “reshut ha-rabim” (“public domain”) which is applied in the laws of Shabbat. And thus the Gemara rules that a public area covered by a roof does not qualify as a “reshut ha-rabim,” because the Israelite camp was not covered. By the same token, according to Rashi (Eiruvin 6a) and several other Rishonim, a public domain cannot qualify as a halakhic “reshut ha-rabim” unless it consists of all least 600,000 people, since the Israelite camp in the wilderness consisted of (roughly) this number of people.
The Shulchan Arukh (O.C. 345:7) cites this view as the second of two opinions. However, as noted by the Arukh Ha-shulchan, Mishna Berura and others, the Shulchan Arukh formulates this view differently than Rashi does. He writes that according to this opinion, a public domain qualifies as a “reshut ha-rabim” only if “600,000 people pass through it each day.” Rather than requiring simply an area with a population of 600,000 people or more, the Shulchan Arukh’s version of this view requires that 600,000 pass through the area every day. This version appears in the Sefer Ha-teruma, as cited in the Beit Yosef (O.C. 345). The Mishkenot Yaakov (O.C. 121) asserts that indeed, different opinions exist in this regard, as some Rishonim require simply the presence of 600,000 people, whereas others require that 600,000 pass through the area each (besides the view taken by the Rambam and others, who require neither condition for an area to qualify as a “reshut ha-rabim”).
The question arises, however, as to the reason underlying this condition, that 600,000 people pass through the area each day. As we noted, the basis for a requirement of 600,000 people is the fact that the Israelite camp in the wilderness serves as the paradigm of a “reshut ha-rabim” for Shabbat. The Israelite camp consisted of 600,000 men, but there is little reason to believe that this number of people left their homes and walked through the camp each day.
The Mishkenot Yaakov (O.C. 120) answers this question on the basis of the Gemara’s comment earlier in Masekhet Shabbat (96b) that the Levites’ section of the Israelite camp was a “reshut ha-rabim.” Rashi explains that the nation’s men would regularly come to be near Moshe, which made the Levite camp a public area. Accordingly, we might explain that it is particularly this area – the area where the Leviyim resided – which establishes the paradigm of a “reshut ha-rabim.” Therefore, since it frequently saw 600,000 people coming in and out, as the people came to be near Moshe and then returned to their tents, some Rishonim understood that a “reshut ha-rabim” requires not the presence of 600,000 people, but rather this number of people passing through on a regular basis.
(See Rav Chaim Leib Eisenstein’s Peninim Mi-bei Midresha, Parashat Bamidbar)