<p>The smallest of the three stone theaters in Rome, built in th S *Campus Martius by L. Cornelius Balbus (minor), probably after his triumph in 19 B.C. (Pliny, <i>NH</i> 5.36-37), as a part of the Augustan program of ‘adorning the city’ (Suet., <i>Aug</i>. 29.4-5: <i>a Cornelio Balbo theatrum</i>). It was dedicated in 13 B.C. during a flood of the Tiber (Dio Cass. 54.25.2), and stood S of the *Porticus Minucia. Like the *Theatrum Pompeium, the <i>cavea</i> of the Theater of Balbus was oriented to face E. A number of its support walls in <i>opus reticulatum</i> have been preserved beneath Palazzo Mattei di Paganica (Richardson, Manacorda, <i>LTUR</i> V). To the E of the stage building stood a large three-sided portico, which came to be known as the ‘<i>crypta Balbi</i>’ (<i>Reg</i>. <i>Cat</i>., <i>Reg. IX</i>; Manacorda, <i>LTUR</i> I). In the center of this portico stood a large rectangular structure of uncertain interpretation, which also seems to have been built by Balbus (Manacorda 1982). The E portion of the complex is shown on the Severan Marble Plan (Rodríguez-Almeida, <i>Forma</i> frags. 30 a,b,c) and its remains are preserved near Via delle Botteghe Oscure. Excavations have shown that earlier residential buildings were destroyed to make room for the portico, and the region immediately to the E of the theater contained a number of private structures by the time Augustan intervention began in this area (Manacorda and Zanini).</p><p><i>Addendum</i></p><p>S. Baiani and M. Ghilardi (edd.), <i>Crypta Balbi, Fori Imperiali: archeologia urbana a Roma</i> (Rome 2000) pl. 1 (depicts orientation of the entire complex at a slight angle toward the Porticus Minucia).</p>