Any enclosure that does not serve a dwelling (like around a garden), and the enclosed area is greater than סאתים, then the Rabbis made a prohibition to carry in such an area more than four amos. However, if the area is a סאתים or less, then it is permitted to carry. The area of a סאתים is 70 amos and 4 tefachim by 70 amos and 4 tefachim (an area of almost 5000 amos). This amount is learned from the size of the Chatzer (100 amos by 50 amos = 5000 amos).
Other measurements are also learned from the size of the courtyard. In determining the extent of a city’s limits in regard to counting the techum of 2000 amos, one needs to determine the exterior limits of the city. The law is that any house within 70 and 2/3 amos of the city’s borders extend the reach of the city to begin the place of the counting of 2000 amos. Again this measurement is learned from the area of the courtyard of the Mishkan.
Another measurement in needed in the law of death of an animal which might be due to slashing of a wild animal. Thus, if a lion enters a “small” area in which an animal (like a cow) is not able to flee, we have to be concerned that the animal has been hurt and would not be kosher even if properly slaughtered later. The size of this “confined” area is an area of 70 and 2/3 amos squared, again learned from the courtyard.
