“For more than 1,500 years the river was known as ”Hebros“. It is assumed that the title is of Thracian origin (Hebros – goat in Thracian) and is associated with the mythology of these ancient inhabitants of our land. […]
According to Professor. St. Mladenov’s research the name “Maritsa” originates from ancient Thracian and relates to the Indo-European root “Mar”, “mer”, which means “swamp”, “lake”, “big water”. To this word’s origin the Slavs added the suffix “itsa” and thus receiving its current name Maritsa1. […]
Today many rivers are called names, originating from old times, when people did not give proper names to the rivers, but marked them with terms that carry meanings like “large water”, “runs”, “floating”, etc. These names later transformed according to the language of the different people who have survived the centuries and are still being used even today. For example, from the Indo-European root “dan”, which means “river”, derived the names of the rivers Don, Danubius (river) and so on. From the same root the Thracian-Phrygian name “Tonzos” comes from which the names of Tunja and Taja originate. All these names simply mean “river”.
1 Mladenov, Assoc., Names of ten Bulgarian rivers, S., 1915, p. 26