Where is Zargrad?

Just like any other collectors of Lithuanian and German stamps, at first, I was assuming that the German name of the Lithuanian city Zarasai during WWII was "Zargrad". It is most probably due to the German stamp catalog Michel which is likely to be the only universal stamp catalog mentioning about the 1941 Zarasai overprinted stamp.

Section of Michel 2009 listing Zarasai (Zargrad) stamps

The strange thing is that I can't find any other historical references mentioning that Zarasai was called Zargrad. This town had many names in the course of history. The oldest official name was probably Jeziorosy, the Polish name, since it was the official language of the Grand Duchy of Lithuania at that time the town was founded. It clearly comes from the word "jezioro" which means "lake" in Polish. So is it Polish? Not so fast... Although the intelligentsia of the country was Polish speaking at that time, many people spoke Lithuanian in forgotten villages across the nation (including part of present Belarus, which you can see from numerous Belarusian villages still bearing names of Lithuanian origin) which is the only factor why the Lithuanian language has been preserved up to the present day. Zarasai was called "Ežerėnai" in Lithuanian which derives from "ežeras" meaning also "lake" like the Polish name. It is not known which one came first to use since there are no Lithuanian written sources mentioning about Zarasai back in those years but linguists suspects that it may have come from a Selonian origin, another now extinct Baltic tribe (Not Slavic!).

  The second change of name came towards the end of the Imperial Russian rule, this time: Новоалександровск / Novoaleksandrovsk. It has been named after the honor of Alexander II of Russia, who later became the Tsar/Emperor of Russia, even though Zarasai was far from being an "Imperial city".

  After WWI, Lithuania regained independence. Logically, the town's name goes back to the Lithuanian name: Ežerėnai, but it looks like they didn't really like the fact that it may have come from a Selonian origin (which is believed to be part of the Latvian ancestry), the town was renamed Zarasai in 1929.

  During WWII, the Germans occupied Lithuania and incorporated within Ostland, and Zarasai was renamed Ossersee (again we see the term "lake" as "see" means lake in German) but the use of Lithuanian name Zarasai was not prohibited. As the war ended, the Soviet authority reinstated the name Зарасай/Zarasai.

So that was the brief history of the name of the town but as you can see, there is no "Zargrad". If indeed Michel had made a mistake, then with which location did they mixed up? My theory surprisingly came up when I was researching about Istanbul, Turkey. Most of the people know that Istanbul was called Constantinople when it was the Imperial capital of the Byzantine Empire. I just happened to try to get informations on Google in Czech language which is called "Cařihrad". Czech is a Slavic language just like Polish or Russian, and I could easily see the similarities between them. "Car" (pronounced "tsar") corresponds to Russian "Tsar", the emperor, and "hrad" is "grad" in Russian like in Lenin-grad or Kalinin-grad, meaning all together the "Imperial city", Tsar-grad. Thinking it should be similar in Polish, I looked at an old Imperial Russian map written in Polish, the area around Novoaleksandrovsk which was the name of Zarasai at that time. And... I've found "Carogród", not far from Zarasai.

The location of Carogród is in Kurland/Courland, which means it was at that time, a German speaking area within the Russian empire. Guess how would you spell the Russian name "Tsargrad" in German? Zargrad!
I went to the english Wikipedia to confirm my discovery but... all it gives me was "Principality of Jersika , an early medieval principality in eastern modern Latvia.". Not only it doesn't give you any reference on why it was called Zargrad in German, the German version doesn't even mention a word of Zargrad and so does the Latvian version. The capital city of the principality called also Jersika is clickable in the english Wikipedia but it gives you the same cr*p (sorry). This is another lesson why you can't trust Wikipedia completely.
Looking at the map carefully, I've found that Carogród is along the railway line Daugavpils (shown as "Dynaburg" on the above map) - Riga to the north west. Now looking at the list of the Imperial Russian railway stations from Daugavpils, and guess what! The third station is "Zargrad"!! Now back to the present map of Latvia hoping that they didn't add any new station... and... Jersika? It looks like a super tiny village but there is a station called Jersika, just like that principality. Now going back to Wikipedia and to look for the entry: Jersika station. Nothing about Zargrad but... clicking the Latvian version, Bingo! "Jersika (stacija), Zargrad in German". Finally...

So my conclusion is:
- The author of Michel probably couldn't find the super tiny village of Jersika.
- Detailed map of the Soviet Union was not much available in the west, including West Germany where Michel was published.
- The closest name to Zargrad nearby was Zarasai.
- Both Zargrad and Novoaleksandrovsk (Zarasai) derives loosely from "Imperial city".
- Both locations have similar distance from Daugavpils.

I think Zargrad must be Jersika, Latvia.  What do you think?