Eruvin 4:8 - 4:9

ואם אינו מכיר – a tree or a fence.

או אינו בקי בהלכה – but he doesn’t know that it will benefit him when he says, that my Sabbath resting place is in a certain place, but he said “my Sabbath resting place is in its place,” he has acquired his place.

עגולות – that regarding the Cities of Refuge, when we appoint them, we derive two thousand cubits of the Sabbath limit, as it is written (Numbers 35:5): “[You shall measure off two thousand cubits outside the town on the east side, two thousand on the south side, two thousand on the west side, and two thousand on the north side, with the town in the center.] That shall be the pasture for their towns.” To this one you give corners (see Talmud Eruvin 51a) which are corner-pieces, but you don’t give corner-pieces to those who set up Sabbath resting places, but the Rabbis who required square expound upon this to include like this (i.e., square) it will be for all Sabbath resting places, and the Halakha is according to the Sages.

כטבלא מרובעת – Maimonides wrote that because it is impossible to make an exactly defined quadrangular, the Mishnah purposely taught "כטבלא מרובעת"/a square board, that is to say, as people are accustomed to make something square, even though it is not an exactly defined quadrangular.

נשכר את הזויות – four corners in its diameter of the quadrangular which is greater than the circle that is within it.

זה שאמרו – such as the case of one who is on the road and he doesn’t have bread with him, and now he is poor, the Sages permitted him to make an Eruv with his feet for Rabbi Meir holds that the essence of the Eruv is with bread and it is a leniency for they were lenient regarding the poor or someone who is coming on the road and he doesn’t have any bread to make an Eruv with his feet. But Rabbi Yehuda holds that the essence of the Eruv is with the foot and it is a leniency, for they made a leniency for the rich who is not able to walk on his feet that he may send his Eruv through an agent and the Halakha is according to Rabbi Yehuda. But both Rabbi Meir and Rabbi Yehuda are similar in that if a person says that his Sabbath resting place is in a certain place, he does not acquire a Sabbath resting place in the place that he said, other than if he is poor or comes on the road and doesn’t have any bread with him, but if he is rich, he must send bread in the place of his Sabbath rest, and he who says: “My Sabbath resting place is in this particular place” does not acquire there a Sabbath resting place other than if there is time left during the day where he can run and arrive there prior to the onset of darkness, and if he lacks that much time left during the day, at the hour that he states: “My Sabbath resting place is in a certain place,” he did not acquire a Sabbath resting place there.