Today, the Sun is observed using different techniques that provide an almost instantaneous 3-D mapping of its structure. Of particular interest is the study of its variability characterised by the 11-year cycle. However, solar activity also varies on longer time scales, as has been attested through indirect methods as the number of sunspots and the records of cosmogenic isotopes, such as 14C and 10Be. The reconstruction of past solar activity may be also complemented by the study of historical accounts. In this book we will describe how these events can be used to obtain information on parameters as solar rotation (sunspot drawings), coronal structure (aurorae and total eclipses) and radius determinations (total eclipses).