also proposed as the cause of the move. Coedes suggested that the move to East Java was probably in response to the Buddhist Shailendra dynasty. This theory is inline with the one proposed by J.G. de Casparis which suggests, that the shift of capital city eastward was to avoid a Srivijaya invasion from Sumatra. However, it was most likely motivated by economic reasons. De Casparis then expands his theory, saying that the location of the kingdom in Central Java was less accessible than East Java. The Brantas river valley was considered to be a strategic location, as the river provides easy access to reach ports on East Java's north coast and Java Sea, strategic for the control of maritime trade routes to the eastern parts of archipelago, being especially vital for control of the Maluku spice trade. This is in contrast with Mataram's Kedu and Kewu Plain that relatively isolated from the north coast of Central Java. Despite its fertility, ideal for rice agricultural kingdom, the Mataram Plain is quite isolated, its northern borders are protected by natural barrier of Merapi, Merbabu, Sumbing, Sundoro, Dieng and Ungaran volcanoes. Ideal for inward-looking agricultural polity, but insufficient to develop a maritime trading kingdom. The recent studies suggest, that the move eastward was not an abrupt event. During the Mataram period in Central Java, the kingdom most likely already expanded eastward and established settlements along Brantas river in East Java. It was more likely that the move was done in gradual manner over long period. The cause of the move was also motivated from multiple factors; either natural, economy or politics. The Sanggurah inscription or popularly known as the "Minto Stone", dated to 982—found in Malang, East Java in early 19th century—mentions the name of a Javanese king, Sri Maharaja Rakai Pangkaja Dyah Wawa Sri Wijayalokanamottungga (King Wawa Wijayaloka), who then ruled the Malang area. This suggests that even during the reign of King Wawa, the Malang region in East Java already belongs within the realm of Mataram Kingdom. The inscription contains elements about the shift of power that consequently took place to East Java. Whatever the true reasons behind the move of political centre from Central to East Java, this event marked the end of an era profoundly. Indeed, the temple-building activity has decreased since the era of King Balitung in scale, quality and quantity, and yet the Eastern Java period of