Nicaea Council -- met in May and June 325 Common Era -- called by Emperor

The Emperor Constantine I called the

Ecumenical Council of Nicaea (modern-day Turkey)

from May 20 until June 19, in the year 325.

Around 300 bishops attended that Council.

See Further:

christianitytoday.com/1990/10/325-first-council-of-nicea/

the modern location is

IZNIK, southeast of Istanbul