The gate | ©Yves Tennevin / CC-BY-SADukes of Lorraine went through this gate after their coronation! Anyway, it was raised in 1603, a year before Saint-Georges gate.
It was named Saint-Nicolas because of Lorraine’s patron saint and because this gate led to Saint-Nicolas-de-Port city!
In the beginning, it was made of a semi-circular arch: the vault disappeared in the 20th century.
The arch was reraised in 1761, to celebrate the visit of king Louis XV’s daughters (and king Stanislas' grand-daughters), Mrs. Adélaide and Victoire: they added Stanislas' chest and the girls' blazons... Oh, they destroyed them during the Revolution.
But we still can see dukes of Lorraine’s coat of arms with Lorraine’s crosses, a helmet and eagles on the lower part of the gate.