There exists a thriving Bronze Age civilization in a gigantic rainforest, bigger than the Amazon and Congo put together. This civilization is built in on the flood plains of a might river system (other questions related here).
Like many other Bronze Age cultures, these people are big on monumental architecture. Unfortunately, there are not a lot of building materials in the rainforest. Sure, there is plenty of wood, but there isn't much stone, and what stone there is must be hauled from thousands of miles away.
I want to build classical Earth's monumental structures, like the mud-brick ziggurats of the Middle East. These structures use fired bricks as the outer surface over a mud brick interior. But, in a land with 2000 mm + per year of rain, these structures would dissolve and wash away in a lifetime.
What materials, available in any rainforest here on Earth, could I use to make bricks? The bricks must be sufficiently durable to last at least thousands of years in a hot humid rainforest, yet sufficiently cheap that a Bronze Age society with a determined priestly/warrior caste could build numerous large temple-palace complexes out of them.