This paper proposes an evolutionary model of spatial economic development in which agglomeration economies and the hub-effect of transport nodes interplay in the making of major cities. The model explains the irreversibility of spatial economic development such as the continuing prosperity of port cities even after their initial advantage of water-access had become irrelevant. It is also shown that in order to decentralize industries from the core region to a periphery region, a temporary protection of industries in the periphery by worsening the transport connection with the core for a short period of time may be desirable.