Because the eruv doesn't just consist of one single unbroken wire. It also often includes natural boundaries like rivers, but also other ones like fences, bridg

Because the eruv doesn't just consist of one single unbroken wire. It also often includes natural boundaries like rivers, but also other ones like fences, bridges and motorways. Often eruvim (plural of eruv) will be built with an irregular shape specifically so they can take advantage of these; thereby reducing the need for new construction.