Bava Batra 12A

בית סתום ⁠– יש לו ארבע אמות; פרץ את פצימיו ⁠– אין לו ארבע אמות.

A house that has a sealed entrance still has the 4 cubits adjoining that entrance because the entrance can be reopened. If one broke its doorposts and sealed the entrance, the entrance is completely negated, and it does not have the 4 cubits adjoining it.

קבר שפתחו סתום ⁠– אינו מטמא כל סביביו; פרץ את פצימיו, וסתמו ⁠– מטמא כל סביביו. בית סתום ⁠– אינו מטמא כל סביביו; פרץ את פצימיו ⁠– מטמא כל סביביו.

There is a similar distinction with regard to the halakhot of ritual impurity. There is a halakha that a house in which there is a corpse transmits ritual impurity only through its doorways. The baraita continues: A grave whose entrance is sealed does not render all its surroundings ritually impure; the ritual impurity extends only to the area opposite the entrance. But if one broke its doorposts and sealed it, it is no longer considered an entrance, and the grave renders all its surroundings ritually impure, because impurity that has no egress bursts from all sides. Similarly, a house in which there is a corpse that has a sealed entrance does not render all its surroundings ritually impure. But if one broke its doorposts, it is no longer considered an entrance, and the corpse renders all of its surroundings ritually impure.

אמר רבה בר בר חנה אמר רבי יוחנן: מבואות המפולשות לעיר אחרת, ובקשו בני העיר לסותמן ⁠– בני אותה העיר מעכבין עליהן. לא מיבעי כי ליכא דרכא אחרינא ⁠– דמעכבי, אלא אפילו כי איכא דרכא אחרינא, נמי מעכבי –

Rabba bar bar Ḥana says that R' Yoḥanan says: With regard to alleyways that are open to another city, and through which one would ordinarily travel to reach that other city, if the residents of the city in which the alleyways are located wished to block them off, the residents of the city into which the alleyways open can prevent them from doing so, because they have a right to reach their city via those routes. The Talmud explains: It is not necessary to state that they can prevent them from blocking the alleyways when there is no alternative route to reach their town, but they can prevent them from blocking the alleyways even when there is an alternative route.