The correct answer is D) the city was a political and economic center.
Constantinople was considered Constantine I's greatest achievement because the city was a political and economic center.
Constantine I (280-337) was the first Christian Roman Emperor. He made of Constantinople, today Istambul(Turkey), an important center for politics, economics, culture, architecture, and arts. The Byzantine Empire had in Constantinople a cosmopolitan place where any kind of thoughts and religious could exist with tolerance and respect.