964. Eiruvei Techumin

Eiruvin 6:1

If a person leaves a city on Friday afternoon and he places enough food for two meals some distance from the city but within its Shabbos boundary, he establishes this as his place for Shabbos. This is so even if he ends up returning to the city before Shabbos and sleeps in his own home. The food that he placed is referred to as an eiruv techumin.

Eiruvin 6:2

On Shabbos, one may walk 2,000 cubits (about 2/3 mile) from the location of his eiruv in all directions. Therefore, when one walks 2,000 cubits from his eiruv on Shabbos within the city, he may walk only to his boundary. If the entire city is within his boundary, then it is treated as if it were only four cubits in size (about six feet), and he may continue to the end of his boundary beyond the city.