Amud Bet of this page discusses what structures are considered part of the city, for the purposes of extending city limits and knowing where to begin counting your two thousand amot limit outside the city. One of the buidings discussed is a nefesh. The Gemara explains that a nefeshthat measures four by four amot can be considered part of the city, while one that has only two walls standing cannot.
What is a nefesh? Monumental Second Temple period graves consisted of two parts, a kever and a nefesh. The kever is just what it sounds like: the grave where the person is buried. Sometimes it is above ground, other times it is below. The nefesh is a second section, something that serves some of the functions of a gravestone today. It is on top and often has a shape rising into the sky, to symbolize the soul (nefesh) returning to God. It is an imposing grave marker. One of the more famous graves with a nefesh that we see today is Yad Avshalom in the Kidron Valley. The pointy part on top is the nefesh.
Sometimes a grave survived and the nefesh was destroyed. That is the case with the grave next door to Yad Avshalom, the tomb of the Bnei Hezir.
But why is a nefesh considered part of the city? Rashi explains that it is designed as a dwelling for the guardian of the graves and can be lived in. That makes it a dwelling and therefore part of the city. The only problem is that the nefesh buildings familiar to archaeologists in the land of Israel seem not to have space for a dwelling. A good example is the third grave in the Kidron Valley, Kever Zechariah. It clearly has a nefesh, but one built of solid rock.
So was Rashi basing himself on structures that he saw in France? Was the Gemara discussing structures in Babylonia? Or are there nefesh dwellings that have been found? Any answers appreciated!