The terms concrete and cement are usually used interchangeably in conversation, but they differ significantly. Concrete is the rock-like material we're all familiar with - a combination of paste, sand and coarse aggregates (gravel). Upon curing it creates the incredibly strong rock-like mass we recognise today in many structures - both old and new.  Cement, more accurately referred to as Portland concrete, serves as the adhesive that binds aggregate particles together. Cement gives strength and hardness to concrete through a chemical process known as hydration: when it combines with water in the mixture. In actuality, this process carries on for many years after installation; thus, signifying that ancient structures are even sturdier than their recently-built counterparts!