Roman Forum of Zadar is the largest on the eastern side of the Adriatic sea, founded by the first Roman Emperor Augustus, as shown by two stone inscriptions about its completion dating from the 3rd century.
Ancient Zadar (or Iadera as the Romans would say) was a Roman colony from 48BC until the disintegration of the Roman empire in the 5th century. After a violent earthquake in the 6th century, the buildings surrounding the forum were destroyed. The still standing elements and stones (then used to rebuild) were retrieved for various buildings.
Most striking is the decorative column marking the western side of the forum. Notice the chains still visible on the column. During the Middle Ages it was the 'pillar of shame' used to punish evildoers.
Continuing on the western side of the Forum, you come to the remains of the Capitolium which was an important temple consecrated to Jupiter, Juno and Minerva.
To round out an appreciation of Roman Zadar, take a look at Zadar's Archaeological Museum which displays artifacts from the Roman period as well as a scale model of the original Roman forum.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.