  We study the effect of insoluble surfactants on the wave dynamics of
vertically-falling liquid films. We use three-dimensional numerical simulations
and employ a hybrid interface-tracking/level-set method, taking into account
Marangoni stresses induced by gradients of interfacial surfactant
concentration. Our numerical predictions for the evolution of the
surfactant-free, three-dimensional wave topology are validated against the
experimental work of Park & Nosoko (2003). The addition of surfactants is found
to influence significantly the development of horseshoe-shaped waves. At low
Marangoni numbers, we show that the wave fronts exhibit spanwise oscillations
before eventually acquiring a quasi two-dimensional shape. In addition, the
presence of Marangoni stresses are found to suppress the peaks of the
travelling waves and preceding capillary wave structures. At high Marangoni
numbers, a near complete rigidification of the interface is observed.
