Ah, yes, the Ancient City. Besides having the most creative name in the Bionicle mythos since the Golden Armour, we've seen a lot of hints about what the Ancient City once was, but we haven't exactly delved into the culture and what not. So, with all of the hints of an arena, the reverence of the Mask Makers, the importance of the Protectors, the geographic positioning of the city and the presence of the Temple of Time, I will ask the question: What was going on in there? I'll start us off here with the possible hierarchy of the city itself. It might be possible that the tribes that we see depicted in the animations stood standing even in the City's heyday, especially considering that there's a structure surrounding the shrine of the Golden Mask of Fire. My theory is that the Ancient City is kinda like the Whiterun's Skyforge. It's a source of elemental power that is ideal for maskmaking. Ekimu and Makuta had noticed the presence of this elementally potent forge, so they built their forge around this. This maskmaking hotspot had turned the Ancient City into a city for Okoto's greatest artisans; architects, stonemasons, blacksmiths and most importantly, the revered maskmakers. This city was relatively isolated from the rest of Okoto and the longer and longer that the inhabitants lived in the Ancient City, the more the city's culture would develop and expand from the tribal and agrarian attitude of the rest of the Okotian tribes. So... it's Rapture.