Its source lies in the Bulgarian Rhodope Mountains near the village Arda, part of the municipality of Smolyan.

It flows eastward past Rudozem, Kardzhali and Ivaylovgrad and enters Greece in the northern part of the Evros regional unit.

It flows into the Maritsa on the border of Greece and Turkey, between the Greek village Kastanies and the Turkish city Edirne.

The Bulgarian section is 229 kilometres (142 mi) long,[1] making the Arda the longest river in the Rhodopes.

To cross the ancient roads to the Aegean, several stone bridges were built on the river, impressive in size and architecture.