Have a good idea of what your thesis will be. You may need to tweak your thesis as you go along, but when you do your proposal, you should have a fairly specific question to ask and an idea of what you think the answer might be. For example:
How are the early lawmakers of Rome portrayed in the primary sources? Early Roman lawmakers are portrayed as idealised Republican heroes in the works of Roman historians.
For the sample proposal below, the question and answer are:
Did the Romans plan to conquer North Africa primarily or in part in order to control the olive trade? Since the olive trade was crucial to the Roman economy and the soil in Italy was becoming depleted, the Romans conquered North Africa partially to gain control over its fertile, olive-producing regions. [This thesis turned out to be disproven, by the way!]
Gather your sources. This is an historiographical paper. That means you can't only tell the story or recount the facts; you have to look at how your sources treat the question. What primary sources will you use? Why are they the best ones? What secondary sources ABOUT the primary sources have you found? You need a biography and critique of each of your primary authors or works. What sources have you found to explain the general topic? By the time you present your proposal, you should have compiled at least a partial bibliography.
Rome, North Africa, and the Olive Trade
In the Mediterranean world of 200-40 B.C, olives and olive products were of primary importance for everything from food to sheep dip. As Rome’s population grew, the agricultural potential of Italy was inadequate to provide sufficient supplies of these commodities. Among the things that made the conquest of Africa attractive to Rome were its fertile agricultural areas that could produce large quantities of olives and were close to shipping routes.
The cultivation and use of olives and olive by-products is well-attested in works by Cato the Elder, Varro, and Columella, all with the title On Agriculture. Their detailed instructions on propagating, cultivating, harvesting, and processing olives will give us a picture of land use, farm management, agricultural technology, and labor requirements as well as information about olives and olive trees in particular.
Geography is an important factor in this study from two points of view. First, from an agricultural standpoint, we will look at the availability of arable land in Italy and North Africa. Vernon Carter and Tom Dale have discussed how landforms, land use, and soil management all play crucial roles in civilization, since the strength of any society depends fundamentally on how well it can feed its citizens. Poor soil management, leading to exhaustion of fertile soil, has often been a significant factor in migration and colonization. We will examine in this paper whether, by the end of the Republic, Italian arable lands had been damaged enough to make colonization of fertile areas in North Africa a desirable goal. Second, from a commercial point of view, we will look at the convenience and accessibility of trade routes between Italy and agricultural centers of North Africa. Archaeological reports such as that by L. Ben Lazreg and D. J. Mattingly will inform this discussion, as will books such as Sabloff and Lamberg-Karlovsky’s Ancient Civilization and Trade.
The development of shipping and harbors is another area we must investigate. The types of ships available for trade, their harbor requirements, and cargo loading and off-loading facilities would have determined the feasibility of large-scale trade between Rome and North Africa. Articles such as George Houston’s “Ports in Perspective” will provide archaeological evidence about shipping, harbors, and amphorae for olive oil, all relevant to the olive trade in this period.
Once we have established that olives were important, that Italy’s soil was becoming exhausted while North Africa was still fertile, and that trade from olive-producing areas to Rome was feasible, we must establish whether, in fact, that trade took place and whether it was a conscious factor in Roman designs upon North Africa.
 Marcus Porcius Cato, On Agriculture, transl. William Davis Hooper (London: Heinemann, 1960)
 Marcus Terrentius Varro, On Agriculture, transl. William Davis Hooper (London: Heinemann, 1960)
 Lucius Junius Moderatus Columella, On Agriculture, transl. Harrison Boyd Ash (Cambridge: Harvard University Press, 1968).
 Vernon Gill Carter and Tom Dale, Topsoil and Civilization, Rev. ed. (Norman: University of Oklahoma Press, 1974).
 L. Ben Lazreg and D. J. Mattingly, Leptiminus (Lamta): A Roman Port City in Tunisia, Report no. 1 (Journal of Roman Archaeology supplementary series no. 4. Ann Arbor: Journal of Roman Archaeology, 1992).
 Jeremy A. Sabloff and C.C. Lamberg-Karlovsky, Ancient Civilization and Trade (Albuquerque: University of New Mexico Press, 1975).
 George W. Houston, “Ports in Perspective: Some Comparative Materials on Roman Merchant Ships and Ports” (American Journal of Archaeology v. 92, no. 4, Oct. 1988), 553-564.
Bellum Africum [in] Caesar: Alexandrian War; African War; Spanish War. Translated by
Cato, Marcus Porcius. On Agriculture. Translated by William Davis Hooper (Loeb Classical Library)
Columella, Lucius Junius Moderatus. On Agriculture. Translated by Harrison Boyd Ash (Loeb Classical Library)
Meijer, Fik and Onno van Nijf, eds. Trade, Transport, and Society in the Ancient World: A Sourcebook.
Sallust. Jugurthine War.
Varro, Marcus Terrentius. On Agriculture. Translated by William Davis Hooper (Loeb Classical Library)
Brothwell, Don. R. and Patricia Brothwell. Food in Antiquity: A Survey of the Diet of Early Peoples.
Levy, Jean-Philippe. The Economic Life of the Ancient World. Translated by John G. Biram.
Oliver, Edmund Henry. Roman Economic Conditions to the Close of the Republic.
Tannahill, Reay. Food in History.
Whittaker, C. Land, City, and Trade in the
Boardman, John [et al.]. “The Olive in the
Fulford, Michael. “Economic Interdependence Among Urban Communities of the Roman Mediterranean.” World Archaeology, v. 19, no. 1: Urbanization (June 1987), 58-75.
Fussell, G. E. “Farming Systems of the Classical Era.” Technology and Culture, v. 8, no. 1 (Jan. 1967), 16-44.
Haywood, Richard M. “The Oil of Leptis.” Classical Philology, v. 36, no. 3 (July 1941), 246-256.
Houston, George W. “Ports in Perspective: Some Comparative Materials on Roman Merchant Ships and Ports.” American Journal of Archaeology, v. 92, no. 4 (Oct. 1988), 553-564.
Johnston, Harry H. “The Importance of
Millar, Fergus. “The
Rostovtzeff, Michael I. “The Hellenistic World and its Economic Development.” American Historical Review, v. 41, no. 2 (Jan. 1936), 231-252.
Townsend, Prescott W. “The Oil Tribute of
Tyree, E. Loeta. and Evangelia Stefanoudaki. “The Olive Pit and Roman Oil Making.” The Biblical Archaeologist, v. 59, no. 3 (Sept. 1996), 171-178.