for support.  On June 11, the number of people allowed on the bridge at one time was reduced, but the lateral shaking periodically reoccurred.  On June 12, 2000, the bridge was closed and an extensive analysis and study of the vibration phenomena began.  Dallard, Fitzpatrick et al (2001) [1] report on the bridge design and the subsequent extensive research that transpired after the bridge was closed.  The severity of the problem was exacerbated by the ever-prolific media, with press headlines such as these: “Wobbling Bridge Will Stay Shut”  – BBC NEWS “£2 Million to Fix the Wibbly Wobbly Way and it Won’t Open Until the Spring” – DAILY PRESS “The Sleek New Footbridge Across the Thames Swayed and Wobbled in the Wind so Much that Some Feared London’s Bridge was Falling Down” – WASHINGTON POST THE PROBLEM The phenomena of forced harmonic excitation of bridge structures is well understood, and has been well documented by many sources.  Most military manuals dating back well into the 1800’s have warnings about soldiers marching in step over bridges of any type.  This was true even for substantial bridges.  For example, in 1860 the famous 1854 Roebling two-deck railway suspension bridge across the Niagara River at Niagara Falls, NY USA was posted with a warning notice to pedestrians against walking in-step.  This heavily built, record-setting span is depicted in Figure 2, from an 1850's engraving.  The warning notice, reproduced from period photographs, is shown in Figure 3. FIGURE 1 THE MILLENNIUM BRIDGE