The today's name of Dubrovnik is derived from the Croatian word Dubrava, which means oak woods as, in the past, oak trees surrounded Dubrovnik. The Latin name Ragusa - Rausa, in use until the 15th century, originated from the rock (lat. Lausa - meaning rock) where the first settlement was established. Dubrovnik was founded in the first half of the 7th century by a group of refugees from Epidaurum (today's Cavtat). They established their settlement at the island and named it Laus. Opposite of that location, at the foot of Srð Mountain, Slavs developed their own settlement under the name of Dubrovnik (named by "Dub" - type of wood). The settlements were separated by a channel which was filled in 12th century, present Placa or Stradun, and since than the two settlements have been united. At that time the city walls started to be built as a protection from different enemies ( Arabs, Venetian, Macedonians, Serbs, etc.), who wanted to conquer Dubrovnik.