Ston (pronounced [stɔ̂n]) is a settlement and a municipality in the Dubrovnik-Neretva County of Croatia, located at the south of isthmus of the Pelješac peninsula.

Because of its geopolitical and strategic position, Ston has had a rich history since ancient times. Located at the gates of the peninsula, surrounded by three seas, protected by four hills, rich in fresh water and saltwater, fertile plains, it has been an important political, cultural and ecclesiastical centre.

Initially it was an Illyrian settlement until the Romans established their own colony there, in 167 BC.

In 533, at Salona, a diocese of Sarsenterum was established for the Zachlumia (Hum) area, which belonged to the church in Ston (Pardui). Later Sarsenterum was destroyed, most likely at the time of the Avars' campaign. Since Ston was not reached by the Avars, it was spared and became the seat of the local župa.

Upon the arrival of the South Slavs in the 7th century, the area of the Neretva (from the northern Herzegovina mountains to Rijeka Dubrovačka) was organized as the principality of Zachlumia - same as Neretva, Primorje and Zahulje, which also belonged to Ston with Rat (Pelješac) and Mljet. Local rulers acknowledged the supremacy of the Byzantine Empire.

As the secular and ecclesial powers grew, it is assumed that after the disappearance of Sarsenterum, Ston became a local ecclesiastical center. The diocese of Ston is first mentioned in 877, as an institution from an earlier time, and the bishop is listed as a suffragan of the metropolis of Split.

After Mihailo Višević, who ruled Zachlumia in the 10th century and acknowledged the authority of the Bulgarian Emperor Simeon, the territory was ruled over by different dynasties. Around 950, it was briefly ruled by the Serbian Prince Časlav. At the end of the 10th century, Samuilo was the Lord of Zachlumia, and the dukedom belonged to the Doclean King Jovan Vladimir.

With the establishment of the Archdiocese of Ragusa (Dubrovnik) in 1120, Ston became a suffragan of the latter.