This paper presents the results of the flexural testing to destruction of two cast iron girders preserved during the demolition of a railway bridge in Scotland. The 151-year-old girders were reinforced with ultrahigh modulus carbon fiber polymer composite (CFRP) plates in 2004. The CFRP plates on one girder were damaged during the demolition and were rendered completely ineffective before testing. The girders were 9 m long and were be tested in four-point bending to failure which gave a unique opportunity to compare the behavior of unreinforced and reinforced cast iron at full-scale. Fragments of cast iron and CFRP that remained after the flexural testing were be used to prepare test specimens and were used to determine material properties. The tests demonstrated the considerable benefits of CFRP strengthening (an increase in load-bearing capacity of 43.9% and an increase in stiffness of 31%) and confirmed that the CFRP was fully bonded to the cast iron until close to the point of failure. The test results have been compared with theoretical and original design predictions that showed that the theoretical predictions were remarkably accurate and the design predictions were conservative as is required for a safe design. This paper includes details of the girders, the test rig, and test procedure, and presents in detail the test results that include the failure mechanisms and will discuss the benefits obtained from the CFRP strengthening of cast iron girders.