Rome had expanded so mush that he moved the ancient sacred boundary - the pomerium
The remains of the Servian wall suggests that it was built in the 4th Centaury not the 6th centaury
The temple of Diana was seen to be a political move as well as beatifying Rome. As Servius thought that building the temple in Rome meant that it was the capital of the city.
The temple of Diana was built because Ephesus, a major city in Asia minor, was rebuilding their great temple of Artemis. This inspired Servius to build a temple to Diana in Rome.