Following his theory of “Architecturally Defined Space”, the Author has explored various architectural programs – open spaces in nature, cities, villages and individual architectural objects. In addition to architecture in ‘common natural environments’, the Author has studied ‘architecture in extreme climatic conditions’, ‘architecture on water’, ‘architecture in water’, ‘architecture in the air’ and (potentially possible) 'architecture on other Space bodies’. This paper deals with the topic of architecture in large river deltas. Although these deltas have been inhabited since prehistoric times to the present day, large river deltas are extreme natural environments where construction in them is very complex and engineeringly demanding.