Reference for Eruvin 48:6

ולעביד ליה צורת הפתח אפומא דשביל של כרמים אתו גמלי שדיין ליה

a [reed] fence on the river bank,<span class="x" onmousemove="('comment',' Thus treating the area and the path as one domain so that the new fence which is put up for dwelling purposes might serve as a part of the enclosure and, being of the prescribed size, effect the desired permissibility.');">¹³</span> one partition upon another partition,<span class="x" onmousemove="('comment',' The river bank being ten handbreadths high is itself regarded as a fence.');">¹⁴</span> surely, cannot [in such a case, usefully] be put up.<span class="x" onmousemove="('comment',' If it is desired to render a lower fence valid. Any fence round an area that was not originally enclosed for dwelling purposes cannot be rendered valid by merely raising its height. It must first be broken down to the prescribed size and then rebuilt.');">¹⁵</span>

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