THE HISTORIY OF THE KNIGHTS TEMPLAR BY CHARLES ADDISON.

The History of the Knights Templar
by Charles G. Addison
[1842]
This is a mainstream history of the Knights Templars, written in the 19th century. Addison details the rise of the Templars to become, essentially, the first multinational corporation. The Templars were entrusted by the Church and States of Europe to be the spearhead of the crusades. In the process they gained immense wealth and influence, although individual Templars took a vow of poverty. Jerusalem was won and lost several times by the crusaders through the 12th and 13th centuries. Addison notably cites eye-witness descriptions from both the Crusaders and their Moslem opponents to give a well-rounded picture. After the crusades, and the loss of the Holy Land, the Templars began a quick decline from which they never recovered. Accused of heresy and bizarre secret rituals, the Templars were subjected to torture and the stake.
The second portion of the book focuses on Temple Church in London, the English headquarters of the Templars in their prime. Addison details the architecture and history of this edifice. The Temple Church eventually became the center of the legal profession in the City of London, a hostel and school for lawyers. Addison mentions on the title page that he is a member of the 'Inner Temple,' which doesn't mean that he was part of a secret society, but instead qualified to practise law in England.
Addison quotes liberally from contemporary accounts in Latin, Norman French, and Early Modern English (which he thankfully occasionally translates), and includes extensive citations of source documents. If you want to learn the fascinating history of the Knights Templars without any extraneous theorizing, this is an excellent book to start with.