Answer:
   
   The Arba'ah Turim was written by Rabbi Jacob ben Asher. He is also
   sometimes known as The Tur (after the title of his most famous work)
   or as "Ba'al Ha'Turim [Master of the Turim]. He lived from 1270 to
   1343, in Toledo, Spain.
   
   Unlike Maimonides' Mishneh Torah, the Arba'ah Turim covers only those
   areas of Jewish religious law that were in force in the author's time;
   it was written to be a halachic guide to those halachot relevent to
   people living outside of Israel in a time where there is no Temple.
   The Mishneh Torah was designed to be a recapitulation of everything of
   the Oral Torah a common man ought to learn, including all of halachah
   and much of aggadah (non-halachic teachings). The Mishneh Torah is
   therefore wider in scope. Rabbi Jacob did not deal with criminal law,
   let alone with the sacrifices or the Zera'im (agricultural precepts
   that could be observed only in the Holy Land.)
   
   In the Tur, the code is divided into four main topics, each of which
   is divided into a sequence of numbered paragraphs. This roughly
   follows the Mishnah, which has six orders: Zera'im (Seeds;
   agricultural laws); Mo'ed (holidays); Nashim (Women and marriage);
   Neziqim (tort and fisal laws); Qodshim (sacred things; sacrifices,
   kosher, and other such topics); Taharos (ritual purity). Not all of
   these are within the Tur's scope: in fact, for some order, only a
   small part apply: only a small part of Zera'im, the bit about
   blessings and the Shema (Tr Berachot), and only a small part of
   Taharos. If you fold these into the adjacent orders, you have the
   origin of the Four Turim. The four "rows" are:
    1. Orah Hayyim - "The Path of Life". This section deals with worship
       and ritual observance in the home and synagogue, through the
       course of the day, the weekly sabbath and the festival cycle.
    2. Yoreh De'ah - "Teach Knowledge". This section deals with assorted
       ritual prohibitions, especially dietary laws and regulations
       concerning menstrual impurity.
    3. Even Ha-'Ezer - "The Rock of the Helpmate". This section deals
       with marriage, divorce and other issues in family law.
    4. Hoshen Mishpat - "The Breastplate of Judgment". This section deals
       with the administration and adjudication of civil law.
       
   Within each Tur, the topics are broken down into subtopics, which are
   then broken down into sections (simanim) and laws (se'ifim). The
   structure down to the simanim is copied by the Shulchan Aruch and
   therefore played a great role in how halachic study is organized.
   
   Another departure from Maimonides' precedent was the fact that the Tur
   did not limit itself to recording the normative positions, but
   compared the various opinions on any disputed point. The influence of
   the Arba'ah Turim is thus perceptible in its integration of the
   Franco-German and Spanish legal traditions, as well as in its fourfold
   structure, which was later adopted by Rabbi Joseph Caro's Shulkhan
   Arukh, and remains the most widely used structure for the organization
   of law codes and responsa.