Battle of San Jacinto

It is curious how Santa Anna managed to get beaten so badly there.  Obviously, the reason for it was that he wasn't expecting it.  He knew the Texan army was in the area, but he probably did not know their will to fight, nor did he know their true numbers.  For these were kept secret from him. 

All he could know for certain was that Houston retreated continually.  Santa Anna had to know that he was hot on Houston's heels the whole time of the retreat.  For Gen. Houston was in Gonzales at the time of the Alamo.  He had ordered it destroyed, and that the men there were to join him at Gonzales.  But they didn't do that, of course.  Once Houston had found out that the Alamo had fallen, he ordered a retreat.  Not a moment too soon.  Within a day, the Mexican Army was in Gonzales.  Houston had it burned, and it was reported that it was still smoldering when the Mexicans arrived.

Santa Anna had to know that General Houston's army was the last one remaining.  He had just taken the Alamo, and he had ordered Fannin and his men to be executed after having been captured at Goliad.  Victory was all but achieved.  Houston's retreat must have signaled cowardice to him.  That's what the interim President of Texas, David G. Burnet thought.  Burnet had been nearly captured himself just before San Jacinto.  He fled to Galveston Island.  Santa Anna had Harrisburg burned, and continued following Houston.

A key bit of information about Gen. Houston's intentions came to Santa Anna's attention.  But it was false intelligence.  Supposedly, Houston wanted to go to Galveston with Burnet.  It may explain the positioning of Santa Anna's army at San Jacinto.  This position blocks any movement toward Galveston along a land route.  The Mexican general could not know how his navy was not having  success at blockading the coast.  Communications were bad.

His lieutenants protested the positioning of the camp.  It violated military doctrine.

On the other side, waited Gen. Houston.  Carefully screening his position so as to not give away his true numbers, he waited for the right time to attack.   Consequently, Santa Anna may have believed that he faced only a remnant of Houston's forces.  The rest supposedly had gone to Galveston to join Burnet.

Why not believe that Houston would retreat to Galveston?  Wasn't that what he was doing all this time instead of fighting?

A large number of men had come in to reinforce the Mexican side.  But they were tired and needed rest.  A guard was kept up for that night, but there was no attack.  The guard came down, and the Mexicans relaxed.

A look at the terrain shows how Santa Anna could have been surprised.  The area was surrounded by marshes and trees.  There was a depression running right down the center of the peninsula, and may at one time had been a stream.  It may have been as much as 20 feet deep.  This separated the two camps, so Houston's men had to cross this bit of terrain, but while doing so, they wouldn't have been noticed until they were really close to the Mexican lines.  This aided the element of surprise.

The time of the attack was at the siesta, a time of the day taken for rest.  The Mexicans were not expecting the attack.  When it came, it came suddenly.  The battle was over in a mere 18 minutes.

Santa Anna was known to make snap judgments.  He misjudged the enemy due to faulty intelligence and poor communications.  He let down his guard, and didn't follow military doctrine.  The result was a catastrophic loss of life, and his own capture.  His military plans had come to naught.  Texas was free.

Note the roads. On the peninsula towards the bottom, the road splits.  The top branch goes inland, the bottom goes towards the coast.  The Texans are behind the road that goes inland, the Mexican force is on the other side.