The author attempts to map the stages through which the Latin appellative lacerna, ‘an open cloak fastened at the shoulder’, passed to eventually serve as a toponym Βλαχέρναι. In the bilingual times of the Eastern part of the Roman Empire, lacerna was not only known but also adopted into Greek as λακέρνα / λαχέρνα. Having been used during the life span of two generations to designate one of the main relics of the sacred precinct in the north-west of Constantinople — the Ἐσθής, or, rather Ἐσθῆτα, the Robe of the Blessed Virgin, λαχέρνα shed both its Latin origin and precise meaning in the memory lane of a Greek speaker; in a situation of ever diminishing bilingualism, the word came to be used as some kind of a vague proper name for the famous church with its relic. Very soon the word made a step further in the same direction becoming an umbrella place-name for the whole sacred precinct. In the process of adaptation, the beginning of the word underwent a phonetic change to become Βλαχέρναι, with the emerging sound having virtually no palpable cause, be it even that certain parallels for such can be provided. As the name of the district in the capital of Eastern Rome, the word made its return into Latin in the form Vlachernae and due to the significance and celebrity of the place came to enjoy worldwide renown.