Koromačno is a settlement in the southeastern part of the Istrian peninsula, located in the synonymous bay between the woody Ubas peninsula in the west and cape Koromačno in the east. The place was built thanks to cement factory, built in 1925, which used cement clay found on the near-by Gradac hill above Vošćica bay. There was a church of St. Joseph in the center of Koromačno, now out of function.
Some of the most significant archaeological and historical sites of Raša municipality are located near Koromačno. At the end of 1980s in the Koromačno bay a 4th-5th century underwater amphorae site was discovered. An Early Bronze age/Iron Age hill-fort was found on Gradac hill (475 m), destroyed due to cement clay exploitation in the quarry. There was also a medieval tower Turan, owned by the Battiala family, built on the same hill. Facing north from the hill-fort there is a 13th-14th century church of St. John with 14th century frescos. This Romanesque church has a semicircular apse, and a porch and a bell cote on the façade were removed in 1993 during the restoration works.