Regarding the transformation of “Konstantinoupolis” into “Stampolis (Σταμπόλις)”, maybe one should point out the existence of Greek last names like “Stampoles (Σταμπόλης)”, “Stampolides (Σταμπολίδης)” etc. However, there are also similar surname versions in neighboring nations like “Stambolic”, “Stambolitz”, “Stambolinsky”, “Стамболийски”, and “Stambolov”. Probably, that is why modern Greeks consider “Stambol” as a non-Greek innovation, if not Turkish, then surely Slavic. So they dismiss the matter, concluding to the exclusive usage for the “Polis” abbreviation, as a name of the imperial capital, during the Middle Ages. Personally, I'm genuinely curious, not so much as who has come up with the inaccurate idea of “Istanbul”-deriving-from-“Eis ten Polin” in the first place, but why this absurdity has managed to become so widespread of a rumor.
New Rome during the 6th c
In fact, the imperial capital, Constantinople, was surrounded by several cities and towns sharing the same suffix “-polis”, including among others:
Adrianople (Αδριανώ --> Edirne),
Adrianople (Hadrianopolis in Paphlagonia, Ἁδριανούπολις ἑν Παφλαγονίᾳ, modern Eskipazar)
Agathopol (ancient Aulaiou Teihos/Αυλαίου Τείχος),
Alexiopolis (founded during early 12th c, opposite Philippoupolis),
Anastasiopolis (Lagania),
Arcadioupolis (Lüleburgaz),
Argyropolis (Gümüşhane),
Callipoli (--> Geliboli --> Gelibolu),
Christopolis, Khristopolis (former Neapolis, modern Kavala),
Chrysopolis (Skoutari --> Üsküdar),
Claudiopolis (Bolu <-- Poli, Πόλη),
Diocletianopolis (Kastoria),
Dionysopolis (ancient Krounoi, modern Balchik),
Eudoxiopolis (Selybria --> Silivri),
Helenopolis (former Drepanon),
Flaviopolis (ancient Creteia),
Germanicopolis (Gangra),
Gratianoupolis (--> Turkish Igrican, as well as Greek Gratini),
Ionopolis (--> İnebolu, ancient Abonoteichiton/Ἀβωνοτειχιτῶν),
Iuliopolis (Gordiou Komi /Γορδίου Κώμη),
Karapolis/Carapolis (In Haemimontum),
Κharioupolis (--> Hayraboli --> Hayrabolu),
Marcianopolis (Devnya),
Maximianoupolis, aka Mosynopolis (--> Misine Hisar & Messoune),
Maximianopolis in Rhodope,
Neapolis (of Bosporus),
Nicopolis upon Danube,
Nicopolis in Colonia of Pontus,
Nicopolis in Upper Khaldia,
Nicopolis in Phrygia (Acroinon since victory against the Muslims in 740, modern AfyonKarahisar),
Palaeopolis in Lydia (Baliamboli),
Paroecopolis/Parœcopolis (in Sintica, eastern Macedonia),
Parthicopolis (Macedonia Prima),
Philippoupolis (--> Filibe, in Turkish, --> Plovdiv, in Bulgarian),
Plotinoupolis (Didymotikhon/Διδυμότειχον),
Pompeiopolis (Πομπηϊούπολις, ancient Soloi/Σόλοι),
Pompeiopolis (Πομπηϊούπολις, in Paphlagonia),
Sebastopolis (η Πιτυούς στην Βόρειο Λαζική),
Soteriopolis (Σωτηριόπολις, η Πιτυούς στην Αβασγία),
Sozopol (Σωζόπολις, ancient Antheia, later Apollonia),
Theodoropolis (Durostorum/Dorustolum, modern Silistra),
Theodoropolis (Samfrapoli/Safranbolu),
Theodoropolis (Euchaita at Helenopontus),
Theodosiopolis (Roman colony Colonia Claudia Aprensis, later also called Apros or ..Napoli, modern Kermeyan),
Traianoupolis/Trajanopolis.
Ancient coin of the Callipoli city-state
So a plain use of “Polis” would have been rather confusing at least in regions like Aemimontvm, Thrace, Propontis, Bithynia and Paphlagonia. On the other hand, we do know for sure that the citizens of the Empire of Romania, regardless of their nationality, although usually native speakers of Greek – or users of Greek as a second language – tended to alter or abbreviate several place-names in a quite unconventional fashion:
Khersonessos (=“Peninsula”, on Crimea) was called Kherson (Χερσών), acquiring a similar suffix with Andron of the Asian Chalcidica, and of Alexandreia of Syria, which was altered into Alexandron (Αλεξανδρών --> Al Iskandarun, in Arabic (Scandrona in Greek) --> Iskederun, eventually in Turkish).
Gratianoupolis, which came to be called Gratini (--> Igrican),
Kydonia (=“glorious”, deriving from “kudos”) became Khania, under the influence of Arabic (824-961).
Chrysopolis became Skoutari (from the name of a military detachment there), whereas,
Ankhialos (Αγχίαλος) became Akhialo (Αχιαλώ), not a big change in writing, but a great shortening change in sound. Not to mention
Thessalonica, also known as Saloniki, unofficially up to this day, and
Didymoteikhon, alias Demotica.
Maximianoupolis became Mosynopoli.
Adrianople was also referred to as Orestias (maybe Adriano (Αδριανώ), as well --> Edirne , in Turkish).
Ayios Theodoros (honoring Saint Theodore Gavras), became Doros or Doron, being the stronghold of the Pontian Gavras family on Crimea, and also the last Greek – and Gothic – bastion against the Ottomans (up to 1475).
So, firstly Constantinopolis was shortened in Greek into Stampoli. Subsequently, the vulgar name of the imperial capital, “Stampoli”, underwent an Altaic transformation during the 16th c, becoming “Istanbul”, as much as the fancy name of the Slavic town of Velesbud (Велбъжд), that is “Constantinopol”, had also experienced an Altaic transformation during the 14th c, becoming “Kyustendil”, a name used up to now by the Bulgarians (Кюстендил). Cases similar to the “Stampoli” --> “Istanbul” name transformation, are well attested in the Uralic - Altaic Language Group:
Stephanos --> Istvan, in Hungarian
skala --> iskele, in Turkish
Skoutari --> Uskundar, in Turkish
Skopje --> ϋskϋp, in Turkish
Sagalassos --> Aglasun, in Turkish
Gratini --> Igrican, in Turkish
Romania's imperial capital, Stampoli, is also called “Kizil Elma” by the Turks, which means “the Red Apple”, not unlike New York's nickname: “the Big Apple”. Maybe it is because both cities used to share a horce-racing tradition, once valued as an ecumenical heritage, like soccer football today.
the main Hippodrome's gateway
The metropolitan area of Constantinople -that is Propontis, from the Bosporus, to the isle of Lemnos- was guarded by the imperial squadron of the Purple Ensign, comprising elite squadrons, usually graced by the exclusive use of the “greek fire”, a secret weapon of mass-burning, actually an early version of napalm!
Ensign Purpure --> Propontis, Lemnos -
Ensign Sable --> Danube, Black Sea -
Ensign Gules (as a remnant of the fleet of the Italy exarchate, in Ravenna) --> Ionian Sea, Adriatic Sea -
Ensign d'Or (as a remnant of an oriental fleet, operational towards the “Golden Dawn”) --> Cibyrrhaeot Theme, and the Levant -
Ensign Azure (a remnant of the Karavesiani fleet) --> Aegean Sea, as well as the Amalfi Duchy, with it's constant interest for the Aegean Sea, the Archipelago -
Also the early-gone-obsolete Ensign Gules et Or, as a token acquired from the fleet of the Africa exarchate, and the Cappadocian house of Heraclius, in Carthage. In use by various non-subjugated states, like the self-governed Balearic Isles, the emirate/chaliphate of Cordoba, the taifa of Denia, the county of Cataluna/Catalonia, the realm of Aragon, and the principality of Salerno. In use beyond the usual boundaries of the Empire, in the Tyrrhenian Sea and further into the West.