Kota na Bato (fort made of stone), former name was ‚Baluarte‛. This ruins are located beside the Cagayan de Oro – Butuan National Road and inside the property of Carmen Zayas. The ruins have a concave formation made of coral stones. The wall has an approximate thickness of one meter. (Source)

The kota
With the arrival of Muslim scholars from nearby Indonesia, the native Filipinos were introduced to the concept of the Kota or fort. The Muslim Filipinos of the south built strong fortresses called kota or moong to protect their communities. Usually, many of the occupants of these kotas are entire families rather than just warriors. Lords often had their own kotas to assert their right to rule, it served not only as a military installation but as a palace for the local Lord. (Source)

See also Karaang Jasaan