The “long wall” after which Long Wall Street (now often run together as Longwall Street) is named is not the fifteenth-century wall of Magdalen College that dominates the entire length of the street on the east side.
The street gets its name from the older City Wall, which still survives (but cannot be seen from the street itself). This wall separates the back gardens of the houses on the west side of Long Wall Street from New College to the north and St Edmund Hall to the south. The picture below shows this “long wall” from inside New College.
Long Wall Street grew up outside the city wall, on the site of the ditch. The east side of Long Wall Street (where there have virtually never been any houses) was situated in Holywell parish, while the west side was in St Peter-in-the-East parish. Both these parishes have now vanished.