Ohalos, Chapter 17, Mishnah 1. Our Mishnah opens a new subject: a field in which a kever was plowed through. A man was working his field, and, we should hope without knowing it, his plow passed straight through a grave. The Mishnah tells us that such a field now takes on a special status: "hachoresh es hakever, harei zeh oseh beis haperas." By plowing a kever he has turned his field into what Chazal call a beis haperas, a place that is metamei, but only miderabbanan.
Why only miderabbanan and not min haTorah? Because of what the plow itself does. The plowing apparatus is built to tear through and grind up the earth, and when it passes through a kever the bones are broken up so thoroughly that in most cases nothing remains with the shiur of a ki-se'orah, the barley-sized piece of bone that would carry tumah min haTorah. Still, it is entirely possible that somewhere in that field a fragment the size of a se'orah did survive, and we have no way of knowing where it ended up. Therefore the Chachamim instituted a tumah upon the area, and it is called a beis haperas.
Before we go further, a thought that is not so pleasant to say but is worth saying. The sefarim hakedoshim teach that limud haTorah itself is a shmirah. When a person learns these halachos, that learning protects him so that, chas veshalom, such a shailah should never arise in his own life. One of the great rabbanim once faced a very difficult shailah shortly before Pesach, and his reaction was to say about himself: this is my own fault, had I reviewed hilchos Pesach properly, I would never have come into such a question. That is how it works.
What Does "Beis Haperas" Mean?
The Bartenura suggests three derivations for the phrase. One traces it to perisah, spreading out, since the tumah is now spread across the field. A second traces it to poras, breaking, because the bones have been shattered and scattered through the ground; this is the root familiar to us from Maseches Berachos, where the slice separated for hamotzi is called a perusah. A third links it to parsah, a stride, as when a distance is reckoned in parsaos, so many hundreds of paces. And what has walking to do with our field? Once word spread that a certain field, nebach, had a kever plowed through it, passers-by would take a detour around the whole area rather than set foot in it, on account of the tumah.
How Much of the Field Becomes a Beis Haperas?
Here a question presses itself upon us. A field can be enormous. Is every last part of it now under a rabbinic tumah? The Mishnah asks precisely this: "ad kamah", to what distance does this status reach out from the grave he plowed through?
The Mishnah gives us the measurement: "melo ma'anah, meiah amah, beis arba'as se'in." Three pieces of information are packed in here, and we need to see how they combine lema'aseh, so that a man who plowed over a kever can know exactly how much of his field carries this din.
Start with the word ma'anah. A ma'anah is a furrow, the groove the plow gouges as it turns the soil over, and the accepted length of such a furrow is one hundred amos. Its width is obviously nothing of the sort; a hundred amos is simply how long a row runs. Hence "melo ma'anah" teaches this: beginning at the grave and continuing a hundred amos in a straight line, the ground must be treated as a beis haperas. Should he have kept going past a hundred amos, the additional distance need not concern him, since Chazal capped the shiur at a hundred. And should he have halted before reaching a hundred, the din covers only the stretch he actually turned over, ending wherever the plow came to rest. Two possibilities, then, are contained in melo ma'anah: up to the spot where he stopped, or, if he continued, up to the length of an ordinary furrow, which is a hundred amos.
So much for the measurement lengthwise. And how wide? The Bartenura understands the Mishnah to be giving a hundred amos in each direction, a hundred of length together with a hundred of breadth, and he identifies such a square with ground in which four se'in of barley could be planted, a beis arba'as se'in. The arithmetic has a known source: the courtyard of the Mishkan measured a hundred by fifty, and that measure is termed a beis se'asayim, room for sowing two se'in. Double it, and a hundred by a hundred comes out to a beis arba'as se'in.
This point really requires a bit more be'ur, and it is worth returning to it when reviewing. For now let us hold onto the picture: melo ma'anah teaches up to a hundred amos if he plowed a hundred, no further than a hundred if he plowed more, and only as far as he reached if he stopped short, since the standard furrow is a hundred amos. And we must also reckon with the sides, a hundred amos wide, giving an area of a hundred by a hundred, the equivalent of a beis arba'as se'in, the ground needed for four se'ah of barley seed.
All of this is where he plowed straight out from the kever in one direction. Suppose, however, that he plowed a hundred amos out from the kever in each of the four directions. Then the total beis haperas will measure two hundred amos by two hundred amos, since you have four squares of a hundred by a hundred. Picture the kever sitting in the center of a box divided into four squares, each direction contributing its own hundred by hundred.
The Pshat of the Rosh
The Rosh reads the Mishnah more plainly. In his understanding, the beis haperas is nothing more than the furrow he cut. Take the sheet of paper in front of you as the field, and set the kever in its upper left corner. He drives the plow downward along the left edge for a hundred amos; that band of ground, up to a hundred amos, is a beis haperas. Now say he also plowed across the upper edge, starting from that same corner and heading rightward. That band too is a beis haperas. For the Rosh, then, only these two bands bear the tumah: the one running down beside the left edge and the one running across the upper edge.
What, then, is the Mishnah adding with beis arba'ah se'in? The Rosh takes it as a description of the field in which all this is happening: the sheet as a whole, so to speak, holds room for four se'ah of seed, which comes to a hundred amos by a hundred amos. Inside that expanse run the two bands, one stretching a hundred amos downward and one a hundred amos across, and only they are assur.
Reviewing the Words
Let us say the teitch over again. How large is a beis haperas? "Melo ma'anah, meiah amah": as far as the plow's straight row extends, one hundred amos. Plow beyond that and the surplus is not included. Width counts too, another hundred amos. One hundred by one hundred equals a beis arba'as se'in, ground in which four se'ah of barley seed would be sown, and that is the reach of the beis haperas. The Rosh, as explained, limits it to the furrow itself, melo ma'anah meaning that hundred-amah row, the usual length of a plowing line. Return to your sheet of paper: the kever in the upper left corner, one band running down beside the left edge, a second band running across the upper edge toward the right. Those bands are what the Rosh forbids, while the sheet in its entirety, the beis arba'as se'in, is the field the Mishnah is picturing.
Rebbi Yosei's Larger Shiur
"Rebbi Yosei omer, beis chamesh." Rebbi Yosei holds that the area is larger: a space in which five se'ah of barley could be sown becomes a beis haperas. Clearly he maintains that the plow spreads the bone fragments further than the Tanna Kamma reckons. The Bartenura tells us, however, that the halachah does not follow Rebbi Yosei.
Plowing Downhill and Plowing Uphill
The Mishnah continues that these measurements apply "bamoired," when he is plowing downward, on ground that slopes down. It need not be a literal mountain, merely a downward slope, and the mefarshim explain that the same applies when he is plowing on level ground. So whether we take the shiur of the Tanna Kamma, beis arba'as se'in, or that of Rebbi Yosei, beis chamesh se'in, it applies specifically when plowing downhill or straight.
"Uvama'aleh": when the plowing proceeds uphill, the shiur shrinks, and the Mishnah supplies a remarkable way of measuring it. Envision a kever lying low on a slope, with the plow climbing away from it. The Mishnah instructs: "nosein rova karshinin", he puts a rova of karshinin "al borech hamachreishah". Karshinin are a species of seed, ordinarily given to animals as fodder. They appear elsewhere: in Maseches Bava Kamma, in the case of an animal that ate karshinin, and likewise in the laws of terumos uma'asros. The English word is vetch.
He takes a rova, one quarter of a kav, of that seed and sets it on the borech of the machreishah. The machreishah is the plow itself; and the borech? They used a length of wood scooped out inside, with holes pierced along its underside. It was loaded with seed and fastened beneath the plow, so that as the plow advanced the seeds dribbled out bit by bit. Understandably, a freshly loaded dispenser releases a steady stream at first, and then the stream thins, fewer and fewer seeds falling. One keeps going "ad mekom sheyitzmechu", until arriving at the place where the trickle has weakened to the point that only "shelosha karshinin" emerge, one beside the next, so that a mere three vetch plants will come up there. Up to that place, "hu oseh beis haperas": that portion of the field bears the din of a beis haperas, which, as is evident, covers considerably less ground than the earlier shiur.
"Rebbi Yosei omer": in Rebbi Yosei's opinion, uphill plowing carries no shiur at all. He restricts the law of a beis haperas entirely to "bamoired", plowing downhill, or, per the mefarshim, on flat terrain. "Aval lo bama'aleh": when ascending, no part of the field turns into a beis haperas. What is his reasoning? The Bartenura points to the reality of how a plow behaves: "shemiyad hamachreishah nineres", the plow is jolted at once, "im yesh sham etzem nofeil", so a bone lodged in it tumbles out on the spot instead of being strewn over the field. In this ruling too we do not pasken like Rebbi Yosei.
One may ask: why do we not say the same when plowing downhill, that the plow shakes and the bone falls out immediately? The mefarshim explain that when plowing uphill the machreishah shakes far more, since there is far greater pressure and the plowing is much harder work.
Summing Up the Mishnah
We have learned the din of a beis haperas: a kever was plowed through, and we are afraid that bone fragments were scattered somewhere in the field. Even though, as we explained, the odds are that the plow did not reach deep enough to leave a piece of the required shiur, Chazal were exceedingly strict here, for reasons that will emerge later on. The practical result: miderabbanan a kohen may not enter a beis haperas, and one who does enter becomes tamei.
And the shiur? Where a kever was plowed through, the affected ground runs a hundred amos in the direction of his plowing plus a hundred amos across, and that square of a hundred by a hundred amounts to ground for sowing four se'ah of barley. That is for plowing in a single direction; plow outward from the grave in a second direction and a second square of a hundred by a hundred joins it, and plow outward in every direction and the entire beis haperas comes to two hundred amos by two hundred amos, four such squares surrounding the grave. The Rosh's approach is more straightforward: only the furrows themselves, each up to a hundred amos, are a beis haperas, while the beis arba'as se'in portrays the field around them; and the Bartenura's proof holds firm, that a courtyard of the Mishkan measuring a hundred by fifty is called a beis se'asayim, so a hundred squared comes to four se'in. Rebbi Yosei stretches the shiur to ground for sowing five se'ah, but we do not pasken that way. All of this holds for plowing downhill or on level ground. Uphill, the Tanna Kamma's measure is far smaller, extending only until the seeder has slowed enough to drop three karshinin seeds beside one another, whereas Rebbi Yosei maintains that uphill there is no beis haperas whatsoever, since the plow is jolted and any bone falls out immediately. Here as well the psak does not follow Rebbi Yosei.