Over the centuries of its existence the Roman army used a variety of cavalry support units. The early legions were supported by 300 horse formed into a unit called the Ala. In the latter years of the Republic Caesar, for example, employed thousands of allied cavalry. At times, during the empire the role of the cavalry at times diminished to a few hundred support units. This page is not an attempt to describe these cavalry units in detail but is only intended to give a general view of the cavalry units and their sizes relative to the army as a whole.
The basic cavalry soldier was almost always armed with a shield and stabbing spear, supplemented by a sword. The Romans were never noted for using mounted archers, for example. The appearance of the cavalry soldier would surely have changed over time but the figure below would be a good generalization of the soldier at almost any time in Rome's history.
Each Ala had an Aeneator, shown on the left with the curved cavalry horn, an officer and a Vexillarius, shown on the right with the red banner. The small square on the right represents their position.
The basic unit of the cavalry, the decuria, seems to have been the same throughout the legion’s history. It was a formation of 10 men with a Decurio as the commander.
In the drawing to the leftl each horseman is allotted a space of 4’ by 10’. The Decurio is shown positioned to the right of the formation in a file of his own. This formation is 5 horsemen wide by two deep, plus the Decurio; it is 24’ wide and 20’ deep.
The Decuria could also be configured two ways, the first was shon in the detail above and again on the left of this drawing. The other configuration is 2 horsemen wide by 10 deep. In some combinations this arrangement seems to fit better. This formation is 12' wide and 50' deep.
3 Decuriae made up the next largest unit, called the Turma. It would have been comprised of 33 men. The drawing below shows two configurations of the Turma based on the two different ways the Decuria could be arranged.
Ala, wing, was the general term for the cavalry unit in the early legions which was set at about 300. As the number of cavalry increased the Ala came to mean a unit of 300 cavalry within the overall force.
Some sources say that the allied auxiliary cavalry units were divided into Turmae in the Roman model. Certainly the cavalry units that were specifically Roman were organized this way. The drawing on the left shows how the 10 Turmae could be arranged into one Ala. The Turma configurations are based on the 2 deep, 5 abreast formation of the Decuria, 2 Decuriae deep and 5 wide which gives a rectangular formation for the Turma..
In the early armies the entire cavalry force was comprised of a single Ala. If the Ala were to be split so that it could support both flanks then the configuration below could have worked. It is based on the 2 abreast, 5 deep configuration of the Decuriae which creates an almost square Turma. There are 5 Turma on either side, the small red square represents the officers who could have been located at any position.
The standard pre-Marius army was comprised of 4 legions and one Ala. That army is shown in the drawing below.
The legions came to use large numbers of allied cavalry, numbering in the thousands. The drawing below shows one way such a force might have looked if it were organized into Alae. Each of the red boxes represents one Ala of 330 men. The 16 Turmae make up a force of 5,280 men. Three formations are shown. At the top the force is shown divided into two wings of 8 Alae each. These formations are each 8 men deep and measure1,820' wide by 120' deep. Below that are two more compact groupings, 900' wide by 260' deep. And at the bottom is a single massed unit of all 16 Alae.
Even if allied cavalry were not organized into Decuriae, Turmae and Alae, the space the cavalry would have occupied would be roughly the same as shown here.
The following drawing shows a force of 5 post-Marian legions with 5,000 supporting cavalry.
Two Armies with Cavalry
The above drawings of the two armies are deceptive because they are not done to the same scale. The drawing below shows the two armies, pre- and post-Marian at the same scale. It is immeidately obvious that the latter army is much larger.
The Pre-Marius army has a total front of just under 6,000 feet. The Post-Marius army exceeds 8,000 feet. The impact of eschelon tactics in making the formation deeper is also apparent.
© 2003, Gary Brueggeman. All rights reserved world wide. No part of this work may be reproduced in part or whole, in any form or by any means, without permission from the author.