In Italy following the second world war, the Vatican-controlled real-estate developer and contractor Società Generale Immobiliare (SGI) emerged as a major force in the country’s reconstruction process. From its Rome headquarters, the ‘Leviathan’ (as the journalist Antonio Cederna called it) devised, delivered and managed dozens of schemes across the peninsula — from residential and commercial developments to industrial, road transport and water infrastructure. None of this would have been possible without the establishment, immediately after the end of the war, of a centralised administrative system coordinating the work of the company’s 10,000 employees. Making use of the company’s unpublished documents, this article examines the bureaucratisation of SGI’s design and construction processes in the period 1945–73. It looks at the development of the company’s in-house information management system; the criteria it adopted in appointing its architectural staff; the modernisation of the company’s office space in Rome; the predicament of the architects on its payroll; its use of high-profile ‘signature’ architects for prestige projects; and the firm’s later adoption of project management techniques developed in the United States. It also looks at the way that the company exploited national and municipal planning regulations (and the gaps within them) to produce building types and urban configurations not previously seen in Italy. Overall, the article situates SGI’s ‘bureaucratic drift’ in the context of the increasingly corporate and specialised professional world of post-war western architecture.