Arch is most possibly one of the oldest structural forms used for bridge superstructures, especially for masonry bridges. Masonry arch bridges are the longest serving structural systems among the railway bridge population most of which are still performing well. To preserve our heritage and to utilize these bridges to their maximum capacity, understanding the behavior and assessing the integrity of arch bridges is vital. Proper maintenance of these bridges will improve the service life of these structures instead of rebuilding with new structure. In this paper, failure investigations are carried out on an old railway stone masonry arch bridge which is severely damaged due to heavy floods during the monsoon. Due to excessive scouring of the soil, uneven settlement of the piers occurred leading to cracks in the arch barrel which made the train traffic to be stopped. Immediate measures are taken to prevent the failure of arch by erecting temporary supporting of full arch and cement grouting of the cracks in order to restore the traffic limiting to minimum speed. In order to assess the integrity and performance of the arch bridge span during the movement of train traffic, instrumentation and response measurements are carried out during the passage of trains with supports under arch and also during the removal of the temporary supports. Field measurements indicated that the load carrying capacity of the arch is inadequate without the temporary supports. Analytical studies are carried out to design a novel retrofitting system to maintain the integrity of the structure while performing the permanent strengthening of the arch. Responses are measured after novel retrofitting to assess the efficacy of the proposed system during the passage of train traffic. The proposed retrofitting system is found to be effective in providing adequate integrity to the arch with less intervention to stoppage of traffic and river flow which will also be integral part of the permanent strengthening scheme for the arch span.