Samaria, the capital of the northern kingdom of Israel, was well known in Old Testament times. In New Testament times the term Samaria seems to be used of a region. See Luke 17:11; John 4:4-7; Acts 1:8; 8:1,9,14; 9:31; 15:3.
The city of Samaria had been rebuilt by Herod the Great and named Sebaste in honor of the Emperor Augustus. Whether Acts 8:5 has in mind Sebaste or some other city of the region of Samaria is impossible to determine with certainty.
Philip went down to the city of Samaria and proclaimed to them the Christ. (Acts 8:5 ESV)
If we follow the reading “the city of Samaria” we might properly think of Sebaste. There is strong manuscript evidence for this reading. Some manuscripts omit the definite article (the). This would allow the translation we find in the Christian Standard Bible:
Philip went down to a city in Samaria and proclaimed the Messiah to them. (Acts 8:5 CSB)
For the moment I am going to assume that Philip went to the city known as Samaria in Old Testament times, and Sebaste in New Testament times.
Herod the Great built a temple to Augustus with a monumental staircase over the palace area of the Israelite kingdom. The temple was destroyed, but later rebuilt along the same plan by Septimius Severus (emperor, A.D. 193-211). The monumental staircase still stands at the top of the tell.
In addition to the ruins of the temple, other Roman remains at Samaria include a stadium, a forum, a small theater, and a long colonnaded street.
This photo shows a portion of the ruins of the forum and mountains surrounding Samaria.
Everything we have seen that was build by Herod the Great is magnificent, even in ruins. Samaria-Sebaste would have been no exception.