My .02c on unique buildings for the Romans and Germanics:
For the Romans, the basilica. The basilica was the administrative centre of a typical Western Roman city. It was also, outside core Roman territory, a great symbol of Romanness. Basically, if a city had a basilica, then its inhabitants knew that it was a Roman city, governed by Roman law and a centre of Roman cultureunlike the various minor towns and villages that might have surrounded it.
For the Germanics (Germany, Goths, etc.), the mead hall. The early Germanics were not known for their architecture, their art or their literature; they were known for one thing alonetheir prowess on the battlefield. Unlike their Celtic neighbours, they inflicted a horrendous defeat upon Rome when the legions came to conquer Germania as they had conquered Gaul. For centuries, the Germanics were feared as raiders and coveted as mercenaries. With time, they eventually assumed the defence of the Western (and to some extent the Eastern) Roman Empire, and then later took over government of the Western Empire, conquering all before them.
And what was at the heart of this militarism? The relationship between lord and warriors. Loyalty to ones lord was the supreme virtue, and in return for this loyalty, ones lord was expected to win glory and gifts for his followers. And what was most symbolic of this relationship between lord and warriors? The mead hall. This hall was a public display of the lords wealth (and thus his success in battlefor this is where wealth came from) and his glorious reputation. It was also the place where he would feast his warriors and, often, distribute his gifts to them. It was also frequently the place where his warriors would swear their loyalty to him.
I much prefer the mead hall to the *thengaz. The truth is that Germanic societies showed a huge variety of systems of government. The *thengaz only existed in some Germanic cultures during some time periods, and in reality, it was simply a council of potentates/elders, which is really not very uniquethis sort of council can be found in many different cultures under many different names. Sure, it had its own unique Germanic flavour, but thats not enough, IMO, to make it special. The idea that the *thengaz is the heart of modern democracy is really a Romantic Victorian/Edwardian notion that no longer enjoys widespread support.