in the East, Rome's slow-moving infantry legions were often confronted by fast-moving cavalry-troops, and found themselves at a tactical disadvantage. Following Rome's subjugation of the Mediterranean, its navy declined in size although it would undergo short-term upgrading and revitalisation in the late Republic to meet several new demands. Julius Caesar assembled a fleet to cross the English Channel and invade Britannia. Pompey raised a fleet to deal with the Cilician pirates who threatened Rome's Mediterranean trading routes. During the civil war that followed, as many as a thousand ships were either constructed or pressed into service from Greek cities. Social structure Citizen families were headed by the family's oldest male, the pater familias, who was lawfully entitled to exercise complete authority (patria potestas) over family property and all family members. Brutus, co-founder of the Republic, is supposed to have exercised the extreme form of this right when he executed his own sons for treachery. Citizenship offered legal protection and rights, but citizens who offended Rome's traditional moral code could be declared infamous, and lose certain legal and social privileges. Citizenship was also taxable, and undischarged debt was potentially a capital offence. A form of limited, theoretically voluntary slavery (debt bondage, or nexum) allowed wealthy creditors to negotiate payment of debt through bonded service. Poor, landless citizens of the lowest class (proletarii) might contract their sons to a creditor, patron or third party employer to obtain an income, or to pay off family debts. Nexum was only abolished when slave labour became more readily available, most notably during the Punic wars. Slaves were simultaneously family members and family property. They could be bought, sold, acquired through warfare, or born and raised within their master's household. They could also buy their freedom with money saved or the offer of future services as a freedman or woman, and their sons could be eligible for citizenship; this degree of social mobility was unusual in the ancient world. Freed slaves and the master who freed them retained certain legal and moral mutual obligations. This was the bottom rung of one of Rome's fundamental social and economic institutions, the client-patron relationship. At the top rung were the senatorial families of the landowning nobility, both patrician and plebeian, bound by shifting allegiances and mutual competition. A plebiscite of 218 forbade senators and their sons to engage in substantial trade or money-lending. A wealthy equestrian class emerged, not