Consequently, limestone when taken out of the kiln... though its bulk remains the same as before, it is found to have lost about a third of its weight owing to the boiling out of the water. Therefore, its pores being thus opened and its texture rendered loose, it readily mixes with sand, and hence the two materials cohere as they dry, unite with the rubble, and make a solid structure.

Chapter V, Sec. 3 - De architectura (The Ten Books On Architecture) (~ 15BC) - Book II