Family and background
Marcus Licinius Crassus was the second of three sons born to the eminent senator and vir triumphalis Publius Licinius Crassus Dives (consul 97, censor 89 BC). This line was not descended from the Crassi Divites, although often assumed to be. The eldest brother Publius (born c. 116 BC) died shortly before the Italic War and he had the unusual distinction of marrying his wife Tertulla (three times) after she had been first widowed by his eldest brother, then Gaius, his younger. His father and the youngest brother Gaius took their own lives in Rome in winter 87–86 BC to avoid capture when being hunted down by the Marians following their victory in the bellum Octavianum.
There were three main branches of the house of the Licinii Crassi in the 2nd and 1st centuries BC, and many mistakes in identifications and lines have arisen owing to the uniformity of Roman nomenclature, erroneous modern suppositions, and the unevenness of information across the generations. In addition the Dives cognomen of the Crassi Divites means rich or wealthy, and since Marcus Crassus, the subject here, was renowned for his enormous wealth, this has contributed to hasty assumptions that his family belonged to the Divites. But no ancient source accords him or his father the Dives cognomen; in fact, we are explicitly informed that his great wealth was acquired rather than inherited, and that he was raised in modest circumstances.
Crassus' grandfather of the same name, Marcus Licinius Crassus (praetor c.126 BC), was facetiously given the Greek nickname Agelastus (the unlaughing or grim) by his contemporary Gaius Lucilius, the famous inventor of Roman satire, who asserted that he smiled once in his whole life. This grandfather was son of Publius Licinius Crassus (consul 171 BC). The latter's brother Gaius Licinius Crassus (consul 168 BC) produced the third line of Licinii Crassi of the period, the most famous of whom was Lucius Licinius Crassus, the greatest Roman orator before Cicero and the latter's childhood hero and model. Marcus Crassus was also a talented orator and one of the most energetic and active advocates of his time.
Youth and the First Civil War
After the Marian purges and the subsequent sudden death of Gaius Marius, the surviving consul Lucius Cornelius Cinna (father-in-law of Julius Caesar) imposed proscriptions on those surviving Roman senators and equestrians who had supported Lucius Cornelius Sulla in his 88 BC march on Rome and overthrow of the traditional Roman political arrangements.
Cinna's proscription forced Crassus to flee to Hispania. He stayed in Spain from 87-84 BC. Here he recruited 2,500 men (an understrength legion) from his father's clients settled in the area. Crassus used his army to extort money from the local cities to pay for his campaigns. He is even accused of sacking Malaca. After Cinna's death in 84 BC, Crassus went to the Roman province of Africa and joined Metellus Pius, one of Sulla's closest allies. He did not stay there long because of disagreements with Metellus. He sailed his army to Greece and joined Sulla "with whom he stood in a position of special honour".  During Sulla's second civil war, Crassus and Gnaeus Pompey fought a battle in the plain of Spoletium (Spoleto), killed some 3000 of the men of Gnaeus Papirius Carbo, the leader of the Marian forces, and besieged Carinas, a Marian commander.
During the decisive battle outside the Colline Gate Crassus commanded the right flank of Sulla's army. After almost a day of fighting the battle was not going very well for Sulla, his own centre was being pushed back and was on the verge of collapse when he got word from Crassus that he had comprehensively crushed the enemy before him. Now, Crassus wanted to know if Sulla needed a hand, or could his men retire. Sulla told him to advance on the enemy's centre. Sulla also used the news to stiffen the resolve of his own troops. The battle still lasted till the next morning, but in the end the Sullan army emerged victorious. And so Sulla became master of Rome. Sulla's victory and Crassus contribution in achieving it put Crassus in a key position. Sulla was as loyal to his allies as he was cruel towards his enemies and Crassus had been a very loyal ally.
Rise to power and wealth
Marcus Licinius Crassus' next concern was to rebuild the fortunes of his family, which had been confiscated during the Marian-Cinnan proscriptions. Sulla's proscriptions, in which the property of his victims was cheaply auctioned off, found one of the greatest acquirers of this type of property in Crassus: indeed, Sulla was especially supportive of this because he wished to spread around the blame as much as possible, among those unscrupulous enough to do so. Sulla's proscriptions ensured that his survivors would recoup their lost fortunes from the fortunes of wealthy adherents to Gaius Marius or Lucius Cornelius Cinna. Proscriptions meant that their political enemies lost their fortunes and their lives; that their female relatives (notably, widows and widowed daughters) were forbidden to remarry; and that in some cases, their families' hopes of rebuilding their fortunes and political significance were destroyed. Crassus is said to have made part of his money from proscriptions, notably the proscription of one man whose name was not initially on the list of those proscribed but was added by Crassus who coveted the man's fortune.
Crassus's wealth is estimated by Pliny at approximately 200 million sestertii. Plutarch, in his "Life of Crassus," says the wealth of Crassus increased from less than 300 talents at first to 7,100 talents. This represented 229 tonnes of gold, or about 7.4 million troy ounces, worth about $9 billion US dollars today, accounted right before his Parthian expedition, most of which Plutarch declares Crassus got "by fire and war, making the public calamities his greatest source of revenue.".
Some of Crassus' wealth was acquired conventionally, through traffic in slaves, production from silver mines, and speculative real estate purchases. Crassus bought property which was confiscated in proscriptions. He notoriously purchased burnt and collapsed buildings. Plutarch wrote that observing how frequent such occurrences were, he bought slaves 'who were architects and builders.' When he had over 500 slaves he bought houses which had burnt and the adjacent 'ones because their owners would let go at a trifling price.' He bought 'the largest part of Rome' in this way. He bought them on the cheap and rebuilt them with slave labour.
The first ever Roman fire brigade was created by Crassus. He took advantage of the fact that Rome had no fire department, by creating his own brigade—500 men strong—which rushed to burning buildings at the first cry of alarm. Upon arriving at the scene, however, the fire fighters did nothing while Crassus offered to buy the burning building from the distressed property owner, at a cheap price. If the owner refused to sell the property, his men would simply let the structure burn to the ground. After buying many properties this way, he rebuilt them and leased it back to their original owners. 
Crassus assiduously befriended Licinia, a Vestal Virgin, whose valuable property he coveted. Plutarch says: "And yet when he was further on in years, he was accused of criminal intimacy with Licinia, one of the vestal virgins and Licinia was formally prosecuted by a certain Plotius. Now Licinia was the owner of a pleasant villa in the suburbs which Crassus wished to get at a low price, and it was for this reason that he was forever hovering about the woman and paying his court to her, until he fell under the abominable suspicion. And in a way it was his avarice that absolved him from the charge of corrupting the vestal, and he was acquitted by the judges. But he did not let Licinia go until he had acquired her property." 
After rebuilding his fortune, Crassus' next concern was his political career. As a wealthy man in Rome, an adherent of Sulla, and a man who hailed from a line of consuls and praetors, Crassus' political future was apparently assured. His problem was that despite his military successes, he was eclipsed by his contemporary Pompey the Great who blackmailed the dictator Sulla into granting him a triumph for victory in Africa over a rag-tag group of dissident Romans; a first in Roman history on a couple of counts. First, Pompey was not even a praetor, on which grounds a triumph had been denied in 206 BC to the great Scipio Africanus, who had just defeated Hannibal's brother Hasdrubal in Spain and brought Rome the entire province of Hispania. Second, Pompey had defeated fellow Romans, rather than a foreign enemy; however, a quasi-precedent had been set when the consul Lucius Julius Caesar (a relative of Gaius Julius Caesar) had been granted a triumph for a small victory over Italian (non-Roman) peoples in the Social War. Pompey's triumph was the first granted to any Roman for defeating another Roman army. Crassus' rivalry with Pompey and his envy of Pompey's triumph would influence his subsequent career.
Crassus and Spartacus
Crassus was rising steadily up the cursus honorum, the sequence of offices held by Roman citizens seeking political power, when ordinary Roman politics were interrupted by two events, the Third Mithridatic War, and later, the Third Servile War, which was the two-year rebellion of slaves under the leadership of Spartacus (from the summer of 73 BC to the spring of 71 BC). In response to the first threat, Rome's best general, Lucius Licinius Lucullus (consul in 74 BC), was sent to defeat Mithridates, followed shortly by his brother Varro Lucullus (consul in 73 BC, whose daughter Tertulla later became Crassus' wife). Meanwhile, Pompey was fighting in Hispania against Quintus Sertorius, the last effective Marian general, without notable advantage. Pompey succeeded only when Sertorius was assassinated by one of his own commanders. The only source to mention Crassus holding the office of praetor is Appian, and the date appears to be in 73 or possibly 72 BC.
The Senate did not initially take the slave rebellion seriously, until they believed Rome itself was under threat. Crassus offered to equip, train, and lead new troops, at his own expense, after several legions had been defeated and their commanders killed in battle or taken prisoner. Eventually, Crassus was sent into battle against Spartacus by the Senate. At first he had trouble both in anticipating Spartacus' moves and in inspiring his army and strengthening their morale. When a segment of his army fled from battle, abandoning their weapons, Crassus revived the ancient practice of decimation – i.e., executing one out of every ten men, with the victims selected by drawing lots. Plutarch reports that "many things horrible and dreadful to see" occurred during the infliction of punishment, which was witnessed by the rest of Crassus' army. Nevertheless, according to Appian, the troops' fighting spirit improved dramatically thereafter, since Crassus had demonstrated that "he was more dangerous to them than the enemy."
Afterwards, when Spartacus retreated to the Bruttium peninsula in the southwest of Italy, Crassus tried to pen up his armies by building a ditch and a rampart across the peninsula of Rhegium in Bruttium, "from sea to sea." Despite this remarkable feat, Spartacus and part of his army still managed to break out. On the night of a heavy snowstorm, they sneaked through Crassus' lines and made a bridge of dirt and tree branches over the ditch, thus escaping.
Some time later, when the Roman armies led by Pompey and Varro Lucullus were recalled to Italy in support of Crassus, Spartacus decided to fight rather than find himself and his followers trapped between three armies, two of them returning from overseas action. In this last battle, the Battle of the Silarius River, Crassus gained a decisive victory, and captured six thousand slaves alive. During the fighting, Spartacus attempted to kill Crassus personally, slaughtering his way toward the general's position, but he succeeded only in killing two of the centurions guarding Crassus. Spartacus himself is believed to have been killed in the battle, although his body was never recovered. The six thousand captured slaves were crucified along the Via Appia by Crassus' orders. At his command, their bodies were not taken down afterwards but remained rotting along Rome's principal route to the South. This was intended as an object lesson to anyone who might think of rebelling against Rome in the future, particularly of slave insurrections against their owners and masters, the Roman citizens.
Crassus effectively ended the Third Servile War in 71 BC. In Plutarch's account, Crassus "had written to the senate that they must summon Lucullus from Thrace and Pompey from Spain, but he was sorry now that he had done so, and was eager to bring the war to an end before those generals came. He knew that the success would be ascribed to the one who came up with assistance, and not to himself."  He decided to attack a splinter group of rebels. After this Spartacus withdrew to the mountains. Pompey had arrived from Hispania with his veterans and was sent to provide reinforcements. Crassus hurried to seek the final battle, which he won. Pompey arrived in time merely for a mop-up operation against the disorganized and defeated fugitives. Pompey wrote to the Senate that "indeed, Crassus had conquered the slaves, but that he himself had extirpated the war". "Crassus, for all his self-approval, did not venture to ask for the major triumph, and it was thought ignoble and mean in him to celebrate even the minor triumph on foot, called the ovation." 
In Plutarch's account Pompey was asked to stand for the consulship. Crassus wanted to become his colleague and asked Pompey for his assistance; "Pompey received his request gladly (for he was desirous of having Crassus, in some way or other, always in debt to him for some favour), and eagerly promoted his candidature, and finally said in a speech to the assembly that he should be no less grateful to them for the colleague than for the office which he desired."  However, in office they did not remain friendly. They "differed on almost every measure, and by their contentiousness rendered their consulship barren politically and without achievement."  Crassus displayed his wealth by public sacrifices to Hercules and entertained the populace at 10,000 tables and distributing sufficient grain to last each family three months, an act which had the additional ends of performing a previously made religious vow of a tithe to the demigod Hercules and also to gain support among the members of the popular party.
In Appian's account, Crassus ended the rebellion and there was a contention over honours between him and Pompey. Neither men dismissed their armies. Both were candidates for the consulship. Crassus had been praetor as the law of Sulla required. Pompey had been neither praetor nor quaestor, and was only thirty-four years old, but he had promised the plebeian tribunes to restore much of their power which had been taken away by Sulla's constitutional reforms. Even when they were both chosen consuls, they did not dismiss their armies stationed near the city. Pompey said that he was awaiting the return of Metellus for his Spanish triumph; Crassus said that Pompey ought to dismiss his army first. In the end Crassus yielded first, offering Pompey his hand.
Alliance with Pompey and Caesar
In 65 BC, Crassus was elected censor with another conservative, Quintus Lutatius Catulus (Capitolinus), himself son of a consul. During that decade, Crassus was Julius Caesar's patron in all but name, financing Caesar's successful election to become Pontifex Maximus. Caesar had formerly been the priest of Jupiter or flamen dialis, but had been deprived of office by Sulla. Crassus also supported Caesar's efforts to win command of military campaigns. Caesar's mediation between Crassus and Pompey led to the creation of the First Triumvirate in 60/59 BC, consisting of Crassus, Pompey, and Caesar (who became consul in 59). This coalition would last until Crassus' own death.
In 55 BC, after the Triumvirate met at the Lucca Conference, Crassus was again consul with Pompey, and a law was passed assigning the provinces of the two Hispanias and Syria to Pompey and Crassus respectively for five years.
Syrian governorship and death
Crassus received Syria as his province, which promised to be an inexhaustible source of wealth. It might have been, had he not also sought military glory and crossed the Euphrates in an attempt to conquer Parthia. Crassus attacked Parthia not only because of its great source of riches, but because of a desire to match the military victories of his two major rivals, Pompey the Great and Julius Caesar. The king of Armenia, Artavazdes II, offered Crassus the aid of nearly forty thousand troops (ten thousand cataphracts and thirty thousand infantrymen) on the condition that Crassus invaded through Armenia so that the king could not only maintain the upkeep of his own troops but also provide a safer route for his men and Crassus'. Crassus refused, and chose the more direct route by crossing the Euphrates. His legions were defeated at Carrhae (modern Harran in Turkey) in 53 BC by a numerically inferior Parthian force. Crassus' legions were mainly infantry men and were not prepared for the type of swift, cavalry-and-arrow attack in which Parthian troops were particularly adept. The Parthians would get within shooting range, rain a barrage of arrows down upon Crassus's troops, turn, fall back, and charge forth with another attack in the same vein. They were even able to shoot as well backwards as they could forwards, increasing the deadliness of their onslaught. Crassus refused his quaestor Gaius Cassius Longinus's plans to reconstitute the Roman battle line, and remained in the testudo formation, thinking that the Parthians would eventually run out of arrows.
Subsequently Crassus' men, being near mutiny, demanded he parley with the Parthians, who had offered to meet with him. Crassus, despondent at the death of his son Publius in the battle, finally agreed to meet the Parthian general; however, when Crassus mounted a horse to ride to the Parthian camp for a peace negotiation, his junior officer Octavius suspected a Parthian trap and grabbed Crassus' horse by the bridle, instigating a sudden fight with the Parthians that left the Roman party dead, including Crassus. A story later emerged to the effect that after Crassus' death, the Parthians poured molten gold into his mouth as a symbol of his thirst for wealth.
The account given in Plutarch's biography of Crassus also mentions that, during the feasting and revelry in the wedding ceremony of Artavazdes's sister to the Parthian king Orodes II's son and heir Pacorus in the Armenian capital of Artashat, Crassus' head was brought to Orodes II. Both kings were enjoying a performance of Euripides' Greek tragedy The Bacchae when a certain actor of the royal court, named Jason of Tralles, took the head and sang the following verses (also from the Bacchae):
We bring from the mountain
A tendril fresh-cut to the palace
A wonderful prey.
Crassus' head was thus used in place of a prop head representing Pentheus and carried by the heroine of the play, Agave.
Also according to Plutarch, a final mockery was made ridiculing the memory of Crassus, by dressing up a Roman prisoner, Caius Paccianus, who resembled him in appearance, in women's clothing, calling him "Crassus" and "Imperator", and leading him in a spectacular show of a final, mock "triumphal procession", putting to ridiculous use the traditional symbols of Roman triumph and authority.