Bitcoin’s Theodosian walls and Hard Forks
By: Federico Tenga
Tags: Segwit, Hard Fork, Satoshi Nakamoto, Blockchain, Bitcoin

The Thoedosian walls protected Constantinople from externals invaders for over a thousand year, until centuries of artillery progress and technological development made fortifications useless.

We lived the block size drama for more than two years, and every time it seems to have ended, after few months we are back in another Bitcoin civil war. Even if the block size debate splits the community and reduce confidence over the future of the protocol, I still believe that overall it is something positive and necessary for the development of Bitcoin. For example, thanks to all the discussions that the debate has caused, many people started to get informed about very technical aspects of the protocol such as latency in blocks propagation, transaction malleability, fee market, quadratic scaling of hashing time and other things that probably wouldn’t had much attentions otherwise. So, whatever happens, in the end at least it was a useful educational experience.

However, it is not my interest to discuss about the pro and cons of a block size increase since I don’t think it is even the real reason why the community is so divided. I believe that the real split in the Bitcoin community is not big blocks vs SegWit, but much more on whether we can use hard forks as a way to upgrade the protocol.

Many of the criticisms to SegWit are about the extra complexity that it brings as a soft fork, while it will be much cleaner to activate it as a hard fork. On the other side many of the opponents of the block size increase are worried about the risks an hard fork could bring.

Obviously, keeping the code clear sounds like a great deal, not only it makes people run a better software, it also means less the technical debt for the protocol reducing the entry barriers for new developers, but unfortunately things are not that simple, the complexity of Bitcoin is not just about the code.

They very reason why Bitcoin became successful in the first place is because it managed to solve, in a probabilistic way, the Byzantine Generals’ Problem in an open network. How this is achieved it has been explained very well by Satoshi in an old post where he describes a situation with a certain number of Byzantine Generals who coordinate with Proof of Work a brute force attack on the emperor Wi-Fi password. In the same way, the Nakamoto Consensus manages to coordinate the participants of the network to decide which block of the blockchain is valid, creating the security needed to make people feel confident to invest wealth in the system.

Byzantine army crushing the invaders trying to steal Constantinople instead of building their own city

From the Byzantine Empire we can learn not only the value of coordination, but also that of security. Indeed, one of the reasons why the Byzantine capital Constantinople has been, for many centuries, the wealthiest and most populated city in the world, was because it could enjoy the protection of the massive Theodosian walls which protected the city from external invaders for over a thousand years, allowing its people to prosper. One of the drawback of the wall was that it limited the territorial expansion of the city, reducing the space for development to only 12 km², but still they were the best 12 km² in the world to trade and do business.