When, on the 20th of May, our advanced light troops reached the banks of the Chickahominy River at Bottom’s Bridge, they found that this, as well as the railroad bridge about a mile above, had been destroyed by the enemy. The Chickahominy in this vicinity is about 40 feet wide, fringed with a dense growth of heavy forest trees, and bordered by low, marshy bottom-lands, varying from half a mile to a mile in width.
Our operations embraced that part of the river between Bottom’s and Meadow Bridges, which covered the principal approaches to Richmond from the east. Within these limits the firm ground lying above high-water mark seldom approaches near the river on either bank, and no locality was found within this section where the high ground came near the stream Oil both sides. It was subject to frequent, sudden, and great variations in the volume of water, and a rise of a few feet overflowed the bottom-lands on both sides. At low water it could be forded at almost any point, but during high water it rose above a fording stage, and could then be crossed only at the few points where bridges had been constructed. These bridges had all been destroyed by the enemy on our approach, and it was necessary not only to reconstruct these, but to build several others.
The west bank of the river opposite the New and Mechanicsville Bridges was bordered by elevated bluffs, which afforded the enemy commanding positions to fortify, establish his batteries, enfilading the approaches upon the two principal roads to Richmond on our right, and resist the reconstruction of the important bridges. This obliged us to select other less exposed points for our crossings.
As the enemy was not in great force opposite Bottom’s Bridge on the arrival of our left at that point, and as it was important to secure a lodgment upon the right bank before he should have time to concentrate his forces and contest the passage, I forthwith ordered Casey’s division to ford the river and occupy the opposite heights. This was promptly done on the 20th, and reconnaissances were at once pushed out in advance.
These troops were directed to throw up defenses in an advantageous position to secure our left flank. General Heintzelman’s corps was thrown forward in support, and Bottom’s Bridge immediately rebuilt.
In the mean time our center and right were advanced to the river above, and on the 24th we carried the village of Mechanicsville, driving the enemy out with our artillery, and forcing them across the bridge, which they destroyed. General Naglee, on the same day, dislodged a force of the enemy from the vicinity of the “Seven Pines,” on the Bottom’s Bridge road, and our advance on the left secured a strong position near that place. [p.26]
All the information obtained from deserters, negroes, and spies indicated that the enemy occupied in force all the approaches to Richmond from the east, and that be intended to dispute every step of our advance beyond the Chickahominy and the passage of the stream opposite our right. That their army was superior to ours in numbers did not admit of a doubt. Strong defenses had been constructed around Richmond.
Official Records of the Rebellion: Volume Eleven, Chapter 23, Part 1: Peninsular Campaign: Reports, pp.25-26
web page Rickard, J (20 June 2006)