If the columns and their foundations have been designed considering the loads (direct force and moment) from the iron gates then a tie beam at ground level is not necessary.
But a tie beam can help in reducing the foundation width in one direction as this beam will help to prevent overturning in one direction (if the columns are not joined by plinth beams towards wall boundaries). Another benefit of a tie beam is the extra strength provided in case of impact by a vehicle to the columns.