In the year before Constantine's succession, Logudoro and Arborea owed allegiance to the Republic of Genoa and Gallura and Cagliari to that of Pisa.

In 1189, a Pisan fleet under Obert, Margrave of Massa, invaded Cagliari and forced Peter to take flight to the court of his brother in Porto Torres.

The treaty stipulated that Genoese merchants be guaranteed their property, citizenship, tax-free commerce, markets, and rights to justice in Logudoro.

Genoa, not content with an alliance between Constantine and the neutral (neither Pisan- nor Genoese-supporting) William, coerced the former to make war on his erstwhile ally.

William, not quick to forgive, instead invaded Logudoro and took the castle of Goceano, where Constantine's wife Prunisinda was residing.