Steel drums are a distinctively Trinidadian ensemble that evolved from improvised percussion instruments used in Carnival processions. By the late 1930s, bamboo tubes, a traditional instrumental, were supplemented by pieces of metal used percussively; over time, these metal percussion instruments were pitched to produce as many as twenty-some tones. Steel bands were large orchestras of these drums, and were banned by the British colonial authorities. Nevertheless, steel drums spread across the Caribbean, and are now an entrenched part of the culture of Trinidad and Tobago.