By the 1530s, small bands of Portuguese traders and prospectors penetrated the interior regions seeking gold, where they set up garrisons and trading posts at Sena and Tete on the Zambezi River and tried to establish a monopoly over the gold trade. The Portuguese finally entered into direct relations with the Mwenemutapa in the 1560s. However, the Portuguese traders and explorers settled in the coastal strip with greater success, and established strongholds safe from their main rivals in East Africa – the Omani Arabs, including those of Zanzibar.