|The American Thread Mill complex is significant as a major textile mill that contributed to the rapid growth of Willimantic and played an important role in its development as a center of textile manufacturing (Criterion A). Beginning with the construction of Mill No.1 and its accompanying dam and bridge in 1857, the mill harnessed the power of the Willimantic River and provided a livelihood for thousands of workers over several generations. Textile manufacturing was continuous on the site for almost 130 years, beginning with linen, quickly changing to cotton, and eventually switching to synthetic textiles before closing in 1985. Mill No.2, which has visually dominated the mill complex since 1864, was the site of early experimentation with electric lighting, leading to the radically different design of Mill No. 4 (1880) as the first mill building in the world designed for electric lighting. 1 Despite the loss of most of the complex's brick mills, it retains much of its character through the survival of its earlier stone buildings, built of granite gneiss quarried from the banks of the Willimantic River. The buildings are excellent examples of mid to late nineteenth-century industrial architecture using local materials (Criterion C). The early twentieth-century concrete warehouse also remains intact. In addition, the mill property has potential to yield important archaeological resources (Criterion D).