Which time period is explicitly NOT mentioned in discussions of sport facility evolution?

The 21st century is explicitly NOT mentioned in discussions of sport facility evolution primarily because the majority of analyses and historical summaries focus on the earlier periods where the foundations of modern sports facilities were established. Discussions often delve into how ancient societies, like the Greeks and Romans, constructed arenas and stadiums for athletic competitions, and how the Renaissance period brought about architectural advancements that influenced modern facilities. Likewise, the 20th century saw significant developments in technology, design, and management of sports facilities, contributing to the evolution we recognize today.

In contrast, as we are still within the 21st century, it is difficult to fully assess or conclude which trends or innovations will ultimately shape this ongoing period in the context of sports facilities. Therefore, while all other options represent distinct historical epochs that have influenced facility evolution, the 21st century remains a contemporary era in progress, making it less likely to be a focal point in discussions emphasizing historical evolution.