I lived in Germany for five months in 1986, working on an archaeology site near the city of Heilbronn. Along with several of the other (paid) volunteers, I lived in a rented house in nearby Leingarten, a dormitory suburban place (not so different from where I live now) up the valley of the river Lein (or Leinbach) which joins the Neckar just north of Heilbronn.
My landlord's daughter, a student in her mid-twenties (so a few years older than me - I turned 19 while I was living there), lived downstairs, and spurred my teenage imagination by having very loud sex with her boyfriend in the room immediately beneath mine. I have completely forgotten her name, but she and her flatmate and their respective boyfriends would occasionally invite us down to the garden for a neighbourly glass of wine.
One day we got talking about local history. It turned out that Leingarten had originally been two historically distinct municipalities, Schluchtern to the west and Großgartach to the east, which had been merged in the name of administrative efficiency back in 1970. In a local microcosm of the merger between the Grand Duchy of Baden and the Kingdom of Württemberg, Schluchtern had been in Baden in the old days, and Großgartach in Württemberg.
I asked her where the boundary ran? Since 1970 there had been a lot of new build (and looking at Google Maps there seems to have been more since 1986). While the former centres of the two former towns were still fairly clear - clusters of shops around the church and the municipal buildings - it was less obvious where one stopped and the other started.
She smiled and told me that the old boundary actually ran through the house. Precisely where, she wasn't sure, but the house was on the line that had separated Schluchtern from Großgartach until 1970, and Baden from Württemberg until 1945. As a map geek since my childhood, I found this very interesting. Unfortunately the local library had mysteriously run out of historical maps, so I was never able to check it, and the question of whether I really had been living on the boundary line lingered unresolved with me for the next thirty years.
Now, thanks to the internet, you can actually pull up historical maps (I'm using the aptly named Old Maps app on the iPad, but there are many other options) and find more answers. First of all, it turns out that Schluchtern was actually an enclave, a village which was in Baden though surrounded by Württemberg. (German Wikipedia has a very long list of such cases in south-eastern Germany alone.) Here is a detail from Müller's 1812 map of Baden, just a few years after the changes wrought to the German principalities by Napoleon:
It doesn't even show Großgartach, and give the impression that the Schluchtern enclave was basically anywhere in earshot of the church's bells. The spendidly named Geognostic Travel Map of Heidelberg and Vicinity published by Groos in 1830 does give a bit more detail - and, critically, shows Großgartach - but doesn't take us a lot further.
However, an 1843 military map (unfortunately with poor definition) shows a very different boundary. Here the centre of the enclave is distinctly west of the centre of habitation; the line as it runs between the two villages goes more or less north-south, somewhat closer to the centre of Schluchtern than of Großgartach. The enclave itself is not a neat circle but an elongated shape including a couple of hills to the north and a couple of valleys to the south. (Perhaps reinforcing my church bells theory.)
Finally an undated motorists' map (I would say first half of the twentieth century) by Freytag and Berndt gives the clearest picture yet. The shape of the enclave is recognisably similar shape to that shown on the 1843 military map. But the inhabited part of Schluchtern is crammed against the eastern edge, while the western border of the enclave grazes the next town along, Schwaigern ("Schweigern" in earlier maps). Most crucially, the easternmost point of the enclave appears to be very close to the location of the place I was renting in 1986.
So, if we zoom in on Schluchtern/Leingarten as it is today, with the location of my address marked, basically my landlord's daughter's story does look plausible. You have to ignore Bundesstraße 293, the road shown in yellow passing north of the town, which was built only in the 1970s; the road shown in the earlier maps is the one shown below as Eppinger Straße, the former highway from Heilbronn to Karlsruhe in simpler times. Bearing that in mind, and the relative location of the road going north from Großgartach to Kirchhausen, I reckon that the easternmost kink of the enclave's boundary may well have been just about where I was living.
If anyone can suggest an easy way of finding out more, I'd be most grateful!