Theater is the name for it. One of the most famous ones, still in good repair, is at Epidauros. An amphitheater is a Roman, not Greek, invention.
A Greek concert is called an odeon.
odei
In concert halls the walls are made out of acoustic materials. The materials, as well as the amplifier may result in multiple echoes in a concert hall.
Oxford
7000
Well I saw him in September 1975 at De Montfort Hall
George Harrison
Video Concert Hall was created in 1978.
Maverick Concert Hall was created in 1916.
Thessaloniki Concert Hall was created in 2000.
Ermitage - concert hall - was created in 1914.
Sapporo Concert Hall was created in 1997.
Limoges Concert Hall was created in 2007.
Oslo Concert Hall was created in 1966.
Vigadó Concert Hall was created in 1859.
Carnegie Hall Concert was created on 1966-07-25.
Town Hall Concert was created on 1964-04-04.
Vatroslav Lisinski Concert Hall was created in 1973.
The Carnegie Hall Concert was created on 2005-09-26.