Namayan, also called Sapa, Maysapan, and sometimes Lamayan, was an independent indigenous polity on the banks of the Pasig River in the Philippines. It is believed to have achieved its peak in 1175, and to have gone into decline sometime in the 13th century, although it continued to be inhabited until the arrival of European colonizers in the 1570s.

The Pasig River is a water body in the Philippines that connects Laguna de Bay to Manila Bay. Stretching for 25.2 kilometers (15.7 mi), it bisects the Philippine capital of Manila and its surrounding urban area into northern and southern halves. Its major tributaries are the Marikina River and San Juan River. The total drainage basin of the Pasig River, including the basin of Laguna de Bay, covers 4,678 square kilometers (1,806 sq mi).