Question: Where did As I look ahead, I am filled with foreboding; like the Roman, I seem to see the River Tiber foaming with much blood""). come from?
Context: The Pons Agrippae (Bridge of Agrippa) was an ancient bridge across the River Tiber in Rome.  It was located 160 metres above the Ponte Sisto, and is known from an inscribed cippus set up by the curatores riparum during the Principate of the Emperor Claudius, suggesting it was built during or before the reign of Claudius.  It was restored in 147 AD.  The bridge is named after Marcus Vipsanius Agrippa, a close friend of the Emperor Augustus.  Agrippa married Julia, the daughter of Augustus, and the couple lived in a villa on the opposite bank of the River Tiber.  To connect his villa to the Field of Mars, where Agrippa had built several important monuments, it has been suggested that Agrippa constructed the Pons Agrippae. Civitella del Lago is a village in the Italian region of Umbria, administratively a "frazione" of the commune of Baschi.  It is located just above lake Corbara, an artificial lake on the course of the river Tiber.  The inhabitants during the winter are about 300 growing in summer to more than 700.  There are sights of the Tiber valley and the province of Viterbo, and on clear days it is possible to see as far as the hills above the Tyrrhenian Sea. The Navalia was ancient Rome's river port and arsenals, which may also have included a naval dockyard.  It was sited on the left bank of the river Tiber to the south of the Campus Martius.  It is sometimes called the 'Navalia superiora' to distinguish it from another military port further down the Tiber near the Forum Boarium (the 'Navalia inferiora').  Its construction was led by Hermodorus of Salamis in the 2nd century BC. On 20 April 1968, British Member of Parliament Enoch Powell addressed a meeting of the Conservative Political Centre in Birmingham, UK.  His speech strongly criticised Commonwealth immigration to the United Kingdom and the then-proposed Race Relations Bill, and became known as the "Rivers of Blood" speech, although Powell always referred to it as "the Birmingham speech".  The expression "rivers of blood", which did not appear in the original speech, is an allusion to a line from Virgil's "Aeneid" quoted by Powell (""As I look ahead, I am filled with foreboding; like the Roman, I seem to see the River Tiber foaming with much blood""). The Quattro Fontane (the Four Fountains) is an ensemble of four Late Renaissance fountains located at the intersection of Via delle Quattro Fontane and Via del Quirinale in Rome.  They were commissioned by Pope Sixtus V and built at the direction of Muzio Mattei, and were installed between 1588 and 1593.  The figure of one fountain is said to represent the River Tiber, in front of an oak-tree; a she-wolf, the symbol of Rome, was a later addition.  A second fountain represents the River Aniene, a tributary of the Tiber, called Anio in ancient Rome, which provided most Roman aqueducts with water.  Pope Sixtus proposed to build a canal to bring the water of the Aniene to Rome.  The other two fountains feature female figures believed to represent the Goddess Diana; the symbol of Chastity; and the Goddess Juno, the symbol of Strength, but it is possible that they may also represent rivers.  The fountains of the Aniene, Tiber, and Juno are the work of Domenico Fontana.  The fountain of Diana was designed by the painter and architect Pietro da Cortona. The Roman Ghetto or Ghetto of Rome, (Italian: "Ghetto di Roma" ), was a Jewish ghetto established in 1555 in the Rione Sant'Angelo, in Rome, Italy, in the area surrounded by present-day Via del Portico d'Ottavia, Lungotevere dei Cenci, Via del Progresso and Via di Santa Maria del Pianto, close to the River Tiber and the Theatre of Marcellus.  With the exception of brief periods under Napoleon from 1808 to 1815 and under the Roman Republics of 1798-99 and 1849, the ghetto of Rome was controlled by the papacy until the capture of Rome in 1870. Lungotevere (Italian for "Tiber Waterfront") is an alley or boulevard running along the river Tiber within the city of Rome. Claudia Quinta was a Roman matron said to have been instrumental in bringing the goddess Cybele, "Great Mother" of the gods from her shrine in Greek Asia Minor to Rome in 204 BC, during the last years of Rome's Second Punic War against Carthage.  The goddess had been brought in response to dire prodigies, a failed harvest and the advice of various oracles.  Roman histories and stories describe Claudia Quinta as "castissima femina" (purest or most virtuous woman) in Rome, chosen along with Scipio Nasica, Rome's "optimus vir" ("best man") to welcome the goddess.  Gossips had accused Claudia of inchastity; but when the ship that carried the goddess's image up the River Tiber stuck fast on a sandbar, Claudia prayed for the goddess's help, then released and towed the ship single-handed.  This miraculous feat proved Claudia's reputation and the goddess's willingness to become Rome's protector.  Soon after, Rome had a good harvest, then defeated the Carthaginian leader Hannibal.  Accounts of Cybele's arrival and her transformation into Rome's Magna Mater were embellished over time with circumstantial details, and formed part of the goddess's founding festival, Megalesia. Like the Roman: The Life of Enoch Powell is a 1998 book by the English writer Simon Heffer.  It is a biography of the politician Enoch Powell.  The title is taken from Powell's 1968 Rivers of Blood speech when Powell quoted Virgil's "Aeneid": "As I look ahead, I am filled with foreboding; like the Roman, I seem to see the River Tiber foaming with much blood". Latium (Latin: "Lătĭŭm" ] ) is the region of central western Italy in which the city of Rome was founded and grew to be the capital city of the Roman Empire.  Latium was originally a small triangle of fertile, volcanic soil on which resided the tribe of the Latins or Latians.  It was located on the left bank (east and south) of the River Tiber, extending northward to the River Anio (a left-bank tributary of the Tiber) and southeastward to the Pomptina Palus (Pontine Marshes, now the Pontine Fields) as far south as the Circeian promontory.  The right bank of the Tiber was occupied by the Etruscan city of Veii, and the other borders were occupied by Italic tribes.  Subsequently, Rome defeated Veii and then its Italic neighbours, expanding Latium to the Apennine Mountains in the northeast and to the opposite end of the marsh in the southeast.  The modern descendant, the Italian "Regione" of Lazio, also called "Latium" in Latin, and occasionally in modern English, is somewhat larger still, but not as much as double the original Latium.
Answer: from Powell's 1968 Rivers of Blood speech