Of the Ancient Romans and public infrastructure
The city of Rome was a colossal undertaking. At peak the city of ancient Rome had an estimated one million people. We'll use this grand stage as a thought experiment about the requirements for modern society and how they're provided.
The ancient world
To keep citizens alive and well the Romans provided many basic services. Aqueducts were constructed to provide water and sanitation, accessible by public fountains and baths and even plumbing to the lower levels of expensive buildings. These aqueducts were also used for irrigating fields, though local Roman fields were not enough to keep up with the population of Rome itself.
Grain as a basic social safety net was imported and subsidized distribution en masse through complex trading routes (Cura Annonae). Grain was imported from across the empire and stored in what today would still be massive warehouses (Horrea Galbae, distributed amongst the city and the citizens. Water powered mills worked turning tons of grain to flour every day. Whilst not everyone assumed free grain to the least fortunate 200,000 of the city was a selfless act ("Bread and circuses" to keep the population content) that still doesn't minimize the scale of the undertaking at such an early stage of human history.
Roads were constructed to facilitate industry ("All roads lead to Rome") and in use many centuries after their placement. What allowed soldiers to march in a known time from location to location allowed industry to take advantage of the same predictability.
None of these were easy, many of which necessitating and producing scientific and bureaucratic progress. Roman roads aimed for a regulation width. Seed ratios were recorded, analyzed, and interrogated.
Modern governments
Depending on where you live in the world, social safety nets are either a boring but respected aspect of daily life or a fundamental threat to the continuation of democracy. This is not an argument I'll enter into in depth here though my belief is that each person should have the financial equivalent of a 1-up token: universal basic income.
In the modern era certain infrastructure projects were completed at scale thanks to financial, industry, and governmental intervention. Dark fibre, thanks to both the dot com bubble and intelligent forethought, exists across most countries on Earth. The cost of placing fibre is in the logistics and labour, not the materials. Technological progress complicated that however, with various advances allowing for ever more bandwidth along existing active strands.
Stretched analogies could be made between aqueducts and roads of the Roman era and telecommunication technology today, though roads perhaps still make more sense for roads.
The Good Roads Movement pushed for quality roads across America, with the 1919 Motor Transport Corps convoy intended to "test vehicles and dramatize the need for improved roads in the nation". Eisenhower was part of that convoy, eventually making highways a signature of his presidency.
[Eisenhower] thought that an interstate highway system would be beneficial for military operations and would also provide a measure of continued economic growth for the nation.
Given highway improvements were catalyzed as much by the German autobahn and Cold War as industry, perhaps the US government should have had their vehicle army "marching" the roads to ensure quality as the Roman soldiers once did.
Modern individuals
What changes can we make to encourage the same types of infrastructure to evolve for the coming age? We might at first imagine that's difficult to do. I'll assume you're not a billionare, though even a billion only gets you so far compared to the expenditures of a governmental entity (i.e. the Interstate Highway System was estimated at half a trillion 2018 dollars).
Technology has allowed for unexpected changes in infrastructure however. Not only can a digital road be built for free but technology has shown many types of infrastructure as fungible. A telephone carried bits as easily as voice. Screens replaced what used to require a printing press. Radio waves replaced cables. Libraries collapsed into the size of a book and then grew exponentially larger across a billion connected devices.
Finance has also changed the economic incentives around infrastructure. Graphics cards accidentally enabled a supercomputer into every home subsidized by interactive fiction. Cryptocurrencies encouraged massive shifts in both power as well as compute infrastructure as it circumvented the traditional financial establishment.
The purpose and scale of infrastructure now jumps most unexpectedly, deviating wildly from any intended purpose.
What infrastructure are you to {build, repurpose, supplant} today?