The paper reports results on an empirical study of the structural properties of HTML markup in websites. A first large-scale survey is made on 708 contemporary (2019–2020) websites, in order to measure various features related to their size and structure: DOM tree size, maximum degree, depth, diversity of element types and CSS classes, among others. The second part of the study leverages archived pages from the Internet Archive, in order to retrace the evolution of these features over a span of 25 years. The goal of this research is to serve as a reference point for studies that include an empirical evaluation on samples of web pages.