More than a million years ago, social nomadic groups came from Africa (Homo antecesor 790.000 b.C., Deposit of The Big Dolina in Atapuerca) and inhabited banks of rivers and other places. They became "more stable" since they changed their way of living for more sedentary habits: hunting, fishing, recollecting fruits... Their first "housings" were set in caves protected from an aggressive environment. They lived and died in them, therefore their housings were their tombs if they died inside them: nomadic communities moved and left their cave because of different circumstances of surviving (Homo heidelbergensis 300.000 b.C., in the Ravine of the Bones in Atapuerca).
To tell the truth, we cannot call this architecture. This is rather a "protective cave-house": we know nothing about the modification of these caves, about its adequation or its physical compartment.
Human evolution (Extinct Homo sapiens neardentalensis and Homo sapiens sapiens) implies the appearance of artistic expressions.
At the Stone Age relationship between decorative arts and "Architecture" appears for the first time. If we can tell so, caves were decorated with paintings. Ideas of housing, magic and beauty go together. This age -Stone Age- is chronologically divided in three parts: Paleolithic -old stone age-, Mesolithic and Neolithic -new stone age-.