Reference for Eruvin 51:4

א"ל רב פפא לרבא והאמר רב אסי מחיצות אדרכלין לא שמה מחיצה אלמא כיון דלצניעותא עבידא לה לא הויא מחיצה ה"נ כיון דלצניעותא עבידא לא הויא מחיצה

Now is not this [orchard] also<span class="x" onmousemove="('comment',' Since the banqueting hall was built after the orchard had been enclosed.');">⁴</span> like [a town that was first] surrounded [by a wall] and subsequently settled?<span class="x" onmousemove="('comment',' How then could Raba permit the moving of objects on the Sabbath in the orchard?');">⁵</span>

Jastrow