In 1857, Baltimore professionalized its police force. Following trends in New York, Boston, and other cities, Baltimore replaced constables and night watchmen with hundreds of uniformed, salaried, beat-walking officers. Ostensibly well trained, the new patrolmen were tasked with bringing order to a growing city plagued by burglaries, violence, and riots. As Adam Malka writes in The Men of Mobtown: Policing Baltimore in the Age of Slavery and Emancipation, the new police presence was palpable, and “to even a casual observer the officers seemed to represent real change” (65). Yet the next year, when white gangs attacked Black shipcaulkers and their employers in Baltimore shipyards, police deliberately did little to prevent the violence or to arrest the perpetrators. The city's nativist Know-Nothing mayor had filled the police ranks with his supporters, and those officers shared the anti-Black prejudices of the ruffian mobs that wanted to reserve skilled shipyard jobs for whites only. For Baltimore's large free-Black community, professionalized policing did not bring greater safety. Instead, the white gangs and vigilantes who had long terrorized Black residents continued to act with impunity.In the earlier era of constables and night watchmen, Malka explains, white vigilantes had played a central role in enforcing the law in Baltimore. Private citizens, empowered by both statute and custom, arrested or inflicted summary punishments on, alleged Black criminals. Although free Black labor was essential to Baltimore's economy, Maryland's slaveholders viewed free Black people as a destabilizing force that needed to be tightly controlled. Laws limited free Black people's mobility and economic behavior as well as their ability to testify in court. “Legal discrimination not only codified racial inequality but empowered white vigilantes,” Malka writes (169). Because constables were ineffective in preventing crime and apprehending alleged culprits, white vigilantes, with city officials’ tacit approval, filled the void, and a brutal system of popular policing flourished. When professionalized policing finally arrived in Baltimore, the force included many officers who had once been vigilantes themselves and who had no intention of reining in anti-Black vigilantism.After emancipation, Malka argues, Baltimore's all-white police force took on the role of aggressively policing the city's Black community that vigilantes had once played. Because the state revamped its constitution and legal codes in favor of the more universal regime of rights required by the Civil Rights Act of 1866, vigilantism declined, as African Americans could now testify in court against their assailants. But this salutary change was offset by white residents’ fear of the city's growing Black population. Slavery had ended, but racialized assumptions of Black criminality persisted. Nervous citizens demanded that the state forcefully police the Black community. The result was a wave of arrests and incarceration for property crimes and vagrancy. Although African Americans now had enhanced due process protections, all-white juries and judges tipped the scales of justice against them. The Maryland state penitentiary, whose inmates had been mostly white before the Civil War, now filled with Black prisoners. By 1872, over 70 percent of the penitentiary's inmates were Black. Malka notes the cruel irony that for Baltimore's African Americans emancipation and declining vigilante violence went hand in hand with rising rates of incarceration. “The potential for good wages, household respectability, and personal autonomy constituted emancipation's hope,” Malka writes, while “policemen and prisons . . . to black Baltimoreans, represented emancipation's despair” (1).Malka also suggests that white Democrats who opposed Reconstruction in cities and states farther south looked to Baltimore and the rest of Maryland as a model for how policing could be used to subjugate the Black population once Republican rule had ended and their states were “redeemed.” On that point, Malka might have done more to explain how Reconstruction unfolded differently in Baltimore than it did in most cities below the Mason-Dixon Line. Because Maryland never seceded, the Military Reconstruction Acts did not apply there, and as a result Maryland never experienced a sustained period of Republican rule. While the state's legislature did replace the old Black Codes with facially neutral laws, the Democratic majority refused to ratify the Fourteenth and Fifteenth Amendments, so Black Marylanders were among the last African Americans in former slaveholding states to gain the right to vote. With Democrats in charge, Baltimore never experienced Reconstruction's moment of possibility. In New Orleans, for example, where Republican rule took hold, the governor purged ex-Confederates and former Know-Nothings from the city's police force and hired scores of Black officers who patrolled the streets, as well as Black detectives who solved high-profile crimes. Unlike in Maryland, in Louisiana Black men also served as jurors. Louisiana had numerous Black legislators and other officeholders. For a time, Louisiana and other unredeemed states served as a counterpoint to the Baltimore model. It is important to note that the rise of a Black carceral state was not inevitable, even if we know in hindsight that Baltimore's approach eventually took root elsewhere after Reconstruction collapsed.Overall, Malka's The Men of Mobtown is a thoughtful and nuanced monograph that shows how police and prisons replaced vigilantism as a means of race control in the border-state city of Baltimore during the age of emancipation. It is an important addition to the scholarship on the history of policing and the rise of the carceral state.