962. Excluding an Area From the Shittuf

Eiruvin 5:21

The rule about designating an area to exclude from the shittuf was made so that there should be some distinction indicating that it’s the eiruv that enables carrying in a large city that has much traffic. It serves as a reminder since it is prohibited to carry in the place that was excluded and did not participate in the shittuf. Each section – the excluded area and the rest of the city – is distinct.

Eiruvin 5:22

If a city that belongs to many people has one entrance plus a ladder elsewhere, the whole city may be included in the eiruv without excluding any area. This is because a ladder on the wall is not considered a proper entrance. The houses that are excluded from a shittuf don’t have to be facing the city. Even if they face away with their backs toward the city, they may be used as the excluded area, making an eiruv throughout the rest of the city.