The council was attended by about 300 bishops
from across the Roman Empire, especially from
the eastern provinces. Interestingly, the pope at
that time, Pope Sylvester I, was not present at
the council, though he had two representatives.
Although Constantine was also present at the
council, and presided over it as an honorary
president, he left the direction of the theological
debates to the ecclesiastical leaders. One of the
most important outcomes (not my answer)