The production of ancient forge-welded iron cannons across the Indian subcontinent represents one of the most remarkable achievements in pre-industrial metallurgical engineering. Long before modern industrial steel manufacturing or the widespread adoption of liquid cast iron molds in Europe, Indian metal artisans mastered a solid-state thermomechanical process that allowed them to fabricate massive, structurally resilient artillery pieces. Constrained by traditional bloomery furnaces that could not reach the high liquid melting temperature of pure iron ($1540^\circ\text{C}$), craftsmen across Rajasthan, Maharashtra, Karnataka, and the Delhi Sultanate developed an empirical mastery of wrought iron, solid-state diffusion, and heat treatment.
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| A heritage cannon on an old Indian Fort pinterest.com |
The foundational material for these artillery pieces was wrought iron produced directly from iron ore using charcoal-fired bloomery furnaces. This direct-reduction technique produced a porous, sponge-like mass of metallic iron known as a bloom, which was heavily interspersed with liquid silicate slag pockets. Through intensive manual hammering while glowing hot, blacksmiths drove out the bulk of the liquid slag and consolidated the iron into solid bars.
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| Fort Angelo Cannon,Kerala .facing Arabian se built by Portuguese keralatourism.org |
Metallurgical evaluations of surviving historical cannons reveal that Indian bloomery iron was characterized by low carbon content, relatively high phosphorus content, and fine, elongated silicate slag stringers running parallel to the direction of forging. This fibrous microstructure gave the metal exceptional longitudinal tensile strength and high resistance to atmospheric and coastal corrosion.To turn these iron bars into a heavy artillery barrel capable of withstanding extreme internal powder pressures, artisans developed the "stave-and-ring" construction method. Blacksmiths arranged a series of long, longitudinal wrought iron bars or staves around a removable central cylindrical core or mandrel. These staves ran the full length of the intended barrel, forming a smooth, uniform inner bore.Once the inner stave core was set, thick circular iron rings were forged separately. These rings were heated to temperatures between 1000 and $1200 to expand their diameter before being slid over the stave core in a process known as thermal hooping. As the rings cooled, thermal contraction caused them to shrink tightly around the longitudinal staves, exerting strong compressive forces that dramatically improved the barrel's radial pressure resistance.................
The systematic structured cannons with Outer Shrink-Fitted Rings, Longitudinal Iron Staves and Outer Shrink-Fitted Rings, Longitudinal Iron Staves and Outer Shrink-Fitted Rings could not only withstand the temperature without out any metal fatigue but also improved the fire power and durability immune to rusting
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| Rajagopalaswamy Cannon Nayak Period Thanjavur TN en.wikipedia.org |
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| Powerful Jahan Kosha cannon Murshidabad, WB Credit: Getty images |
Above image: Forged in 1637 CE by smith Janardan Karmakar; measures 17.5 feet long and exhibits negligible rust...........
The true core of the technique, however, was solid-state forge welding. The assembled stave-and-ring structure was placed into massive charcoal pit hearths and heated until the iron became plastic. Blacksmiths then vigorously hammered the red-hot outer rings using heavy handheld sledges or drop hammers. By introducing mineral fluxes like borax or silica sand to clean surface oxides from the metal, the intense hammering caused atomic diffusion across the contacting interfaces. This fused the individual rings and staves into a single, cohesive metallic barrel without ever melting the iron into a liquid state.Across the subcontinent, regional powers tailored this technology to their tactical needs and geography:
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| two stage cast bronze iron of Gulbarga KA facebook.com |
Karnataka (Deccan Sultanates): The Deccan region achieved some of the largest scale forge-welded weapons in human history. Fortresses in Bidar, Gulbarga, and Bijapur host massive cannons weighing upwards of 30 to 50 metric tons, constructed via complex multi-layered stave-and-ring assemblies designed to project stone and metal shot over long siege distances.Maharashtra (Maratha & Coastal Forts): Coastal and hilltop fortresses like Daulatabad, Janjira, and Raigad feature cannons adapted to harsh marine environments. In some cases, smiths executed bimetallic forge-welding, combining an inner wrought iron sleeve for high internal pressure strength with an outer cast bronze or copper protective cladding to resist salt air degradation.
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| A cannon on Bidar Fort, Karnataka karnatakatravel.blogspot.com |
Above image: Badi Tope of Bidar Fort the capital of Bahamani kingdom, Karnataka. It is known as "big gun." Positioned strategically on a massive turret to defend the fort's western and southern walls.Borer. length of the cannon is 15 feet.Once mounted on aa swivel mechanism, it could be turned to any direction. Specially constructed wall could present accidental turn toward the fort..Massive Bahmani and Adil Shahi era cannons forged in multi-segment reinforced rings............
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| Mendha cannon navrangindia.blogspot.com |
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| 2nd largest in India Mendha cannon of Daulatabad reddit.com |
Above image: Installed by Mogul ruler Aurangzeb at Aurangabad, Maharashtra state. 17th century Cannon with the rear end shaped like ram's head. second largest canon in India located on the Daulatabad Fort. It was mounted once on a rotating circular platform. Also called breaker of forts(Quila Shikan).........
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| cast in 1720 world's largest Jaivana cannon on wheel Jaigarh fort, Rajasthan lashpackingkerala.com |
Rajasthan (Rajput Arsenals): Hilltop arsenals like Jaigarh Fort in Jaipur housed dedicated foundry complexes. Rajput metallurgists built multi-ring iron cannons with thick breech blocks specifically designed to endure heavy gunpowder loads during prolonged castle sieges.
Delhi Sultanate & Imperial Mughals: Early Delhi Sultanate forces integrated native bloomery traditions to produce long-barreled siege pieces. Imperial workshops refined these designs by welding specialized iron hoops at critical stress points near the combustion chamber, reinforcing the breech against explosive forces.Through the clever integration of thermal hooping, composite microstructures, and solid-state diffusion welding, ancient Indian artisans created monumental weapons that survived centuries of warfare and weather. These massive forge-welded cannons remain an enduring testament to the sophisticated materials science and practical engineering of historic India.
https://www.academia.edu/31183123/Forge_Welded_Iron_Cannon_in_Medieval_Deccan_Forts#:~:text
https://ghadar.org.in/2009/10/20/the-rise-and-fall-of-ancient-indias-iron-and-steel-metallurgy/#:~
Primary Archaeological & Metallurgical Literature:
Balasubramaniam, R. "A Marvel of Medieval Indian Metallurgy: Thanjavur's Forge-Welded Iron Cannon." Indian Journal of History of Science.
Singh, M. Rajdeo. "Microstructural Studies of Composite Mughal Period Cannons of Daulatabad Fort, India." National Museum Institute / Journal of Archaeometry.
Biswas, A. K. "Minerals and Metals in Ancient India." Trust for Oriental Research.
K. N. Jayaraman (Author: navrangindia.blogspot.com)
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