What religion did constantine recognize as a legal religion

Christianity

Explanation:

Rome used to be a jewish country. However, in the year 313, the emperor Constantine issued the Edict of Milan, which granted Christianity legal status.

The Edict of Milan was an agreement to treat Christians benevolently within the Roman Empire, since they had been subjects of torture and persecution in Rome since the beginning of Christianity. This Edict required that the wrong done to the Christians be righted as thoroughly as possible.

And although this Edict gave Christianity legal status, it was not until the year 380 that Christianity actually became the official religion of the Roman Empire.

However, it was this Edict issued by Constantine the one that gave legal status to Christianity.