<P> In an attempt to secure their future, steamboat interests successfully lobbied to place restrictions on bridge construction, requiring spans and heights previously unheard of . This was ostensibly to maintain sufficient operating room for steamboats beneath the bridge's base for the then foreseeable future . The unproclaimed purpose was to require a bridge so grand and lofty that it was impossible to erect according to conventional building techniques . The steamboat parties planned to prevent any structure from being built, in order to ensure continued dependence on river traffic to sustain commerce in the region . </P> <P> Such a bridge required a radical design solution . The Mississippi River's current was almost 12 ⁄ feet per second (3.8 m / s) and the builders had to battle ice floes in the winter . The ribbed arch had been a known construction technique for centuries . The triple span, tubular metallic arch construction was supported by two shore abutments and two mid-river piers . Four pairs of arches per span (upper and lower) were set eight feet (2.4 m) apart, supporting an upper deck for vehicular traffic and a lower deck for rail traffic . </P> <P> Construction involved varied and confusing design elements and pressures . State and federal charters precluded suspension or draw bridges, or wood construction . There were constraints on span size and the height above the water line . The location dictated reconciling differences in heights from the low Illinois floodplain of the east bank to the high Missouri cliff on the west bank of the river . The bedrock required deep drilling to reach, as it was 38 m below water level on the Illinois side and 26 m below on the Missouri side . </P> <P> These pressures resulted in a bridge noted as innovative for precision and accuracy of construction and quality control . This was the first use of structural alloy steel in a major building construction, through use of cast chromium steel components . The completed bridge also relied on significant--and unknown--amounts of wrought iron . Eads argued that the great compressive strength of steel was ideal for use in the upright arch design . This decision resulted from a curious combination of chance and necessity, due to the insufficient strength of alternative material choices . </P>

Who built the first bridge across the mississippi river