Why did romans begin to utilize travertine in the late 2nd century b. c.e?

Long before concrete made its appearance on the building scene in Rome, the Romans utilized a volcanic stone native to Italy called tufa to construct their buildings. Although tufa never went out of use, travertine began to be utilized in the late 2nd century B.C.E. because it was more durable.

Idont know what to do here

Where are the following