A reshut ha-yaĥid is an area enclosed by walls, which render it a single place, and one may carry objects in this enclosed area. Even a large area surrounded by walls is considered one place, and there is no fundamental difference whether an object is located on its east or west side.
The classic example of a reshut ha-yaĥid is a house, though an area may be considered a reshut ha-yaĥid even without a roof. As long as it is enclosed by a barrier ten tefaĥim high (76 cm), it is a reshut ha-yaĥid. A pit that is ten tefaĥim deep is also considered a reshut ha-yaĥid, as is a rock or hill that is ten tefaĥim high. Even if there are no walls surrounding the rock or hill, the fact that they are raised ten tefaĥim from the ground puts them in the same category as something walled. We treat them as if they have walls that extend upward beyond the top of the rock or hill. To be defined as a reshut ha-yaĥid, an area must be at least four tefaĥim wide (about 30 cm). Lacking this width, the area is not significant enough to be deemed a reshut ha-yaĥid, only a mekom petur. It should be noted that a sharp incline is considered a wall as well.
A reshut ha-rabim is an area that serves public needs such as streets, squares, markets, and intercity roads. To qualify as a reshut ha-rabim, an area must be at least 16 amot wide, and unroofed. Some add an additional condition: every day it must be traversed by 600,000 people, equivalent to the number of Israelites during our ancestors’ travels in the desert, according to the Torah (see section 8 below). In principle, all prohibitions on carrying are connected to reshut ha-rabim. Formulated in the negative, there is no Torah prohibition on carrying where there is no reshut ha-rabim. Within a reshut ha-rabim, one may not carry an object more than four amot (see sections 3-4 below), and one may not transport an object from a reshut ha-yaĥid to a reshut ha-rabim and vice versa.
. If the slope surrounding a hill is steep enough (it declines ten tefaĥim vertically within four amot [ 182.4 cm] horizontally), it is considered a wall, which makes everything atop the slope into a reshut ha-yaĥid. The Sages refer to such a hill as a tel ha-mitlaket (MB 345:5; there is disagreement about whether the slope itself is considered a part of the reshut ha-yaĥid, as explained in BHL 352:2 s.v. “be-inyan”). The same rule applies to a valley that is surrounded by a slope of such steepness.The Sages ordained that if a place surrounded by walls is larger than beit satayim, even though according to Torah law it is still a reshut ha-yaĥid, one may carry within it only if its walls were made for residential purposes. If they are natural walls, one must put up a new wall that is wider than ten amot and at a distance of less than ten amot from the natural wall, so that people have participated in the surrounding wall. Then one may carry in the entire area (SA 358:8; MB ad loc. 62). Beit satayim is the size of the courtyard of the Mishkan, the dimensions of which were 50 amot by 100 amot (5,000 square amot). That translates into 1039.68 square meters, or a little more than a dunam (about a quarter of an acre).
The exact size of a tefaĥ is the width of the hand across the knuckles that connect the four fingers (excluding the thumb) to the palm, or approximately 7.6 cm (see below ch. 29 n. 1). Accordingly, three tefaĥim are 22.8 cm. I rounded it off to 23 in the text of this chapter (sections 3 and 7) to make it easier to remember. Four tefaĥim are 30.4 cm, and I rounded it off to 30. Similarly, 16 amot are 7.296 m, which I round off to 7.3.