Take the concept down to the systems of daily life.

Marius Arc does not place 100,000 people in one enormous room. Residential blocks of roughly 400 to 800 people form the basic unit, with schools, clinics, shared kitchens, laundries, repair shops and planted gardens within walking distance. Most errands fit inside a fifteen-minute range; trunk transit is reserved for commercial districts and the spaceport.

Each block can isolate behind airtight bulkheads without becoming closed in daily life. Circular passenger routes, back-of-house logistics and public squares overlap, while emergency plans can separate people from freight. Local councils decide shared-space rules and service priorities, making residents participants in city operations.

Food is designed for pleasure as well as nutrition. Greenhouse vegetables, mushrooms, algae, fermented proteins and cultivated meat become bread, noodles, soups, side dishes and sweets. Convenience stores carry single-meal packs and reusable trays, reducing household refrigeration and waste while increasing everyday choice.

Schools teach lunar materials, plants, maintenance and low-gravity physiology alongside Earth history. Parks and sports turn one-sixth gravity into play, while medicine follows growth, pregnancy and ageing over decades. Birth, education, work, care and remembrance must all exist before the Moon can be called home.

Life support, the spaceport, power and mining require three-shift supervision. Yet teachers, nurses, cooks, carers, designers, theatre technicians, cleaners, couriers and sports coaches sustain most of urban life. Robots take hazardous tasks, while judgement, teaching and care remain human professions.

On the Moon, the ability to diagnose, repair and remanufacture is more valuable than waiting for replacement parts from Earth. Vocational education moves among schools, workshops and employers, with qualifications recognised in both worlds. Shops and cultural work need viable incomes so the economy does not become a single infrastructure industry.

The natural lava tube absorbs radiation, temperature swings and micrometeorites, but it is never the room itself. An independent pressure shell sits inside the rock with insulation, utility layers and replaceable interior panels. Every wall and ceiling people touch can be cleaned, inspected and repaired.

Airtight bulkheads divide habitation into small zones and close automatically during depressurisation. Water, air and power run through service spines behind living spaces, so maintenance does not require demolishing a home. Multiple neighbouring refuge zones prevent one fault from stopping the whole city.

Wastewater, plant transpiration and air-conditioning condensate are recovered and purified. Leakage, growth and strategic storage still require new supply, so the city processes lunar ice and can synthesise water from oxygen and hydrogen. Drinking, agriculture, industry and emergency reserves use separate quality and priority loops.

Solar fields, storage and fusion divide the power load, with independent emergency circuits for farms, medicine and communications. Waste returns as fermentation feedstock, fertiliser, polymers or building material; only unusable residue is stabilised. The real measure is not recycling alone, but the ability to keep living through a failure.

Large Earth transports transfer at a cislunar station rather than landing directly. Passengers and cargo continue in separate vehicles: people move from the lunar spaceport into underground transit, while materials enter logistics lines that bypass homes. Study, work, family visits and tourism become ordinary reasons to travel.

Growth does not mean filling one cavity forever. Excavation, pressure shells, life support and public facilities are standardised so small self-sufficient colonies can open in sequence. Each generation uses more lunar metal, glass and ceramic, then connects completed settlements through transport and communications.