Swimming near solid boundaries, E. coli exhibits clockwise circular motion. This behavior is explained by a hydrodynamic model that accounts for force-free and torque-free swimming, as well as hydrodynamic interactions with the boundary. The model shows that the radius of curvature of the trajectory increases with the length of the bacterium. Experimental data on E. coli swimming near glass surfaces confirm this behavior, with the radius of curvature increasing with cell size. The model also predicts that cells swim into the surface due to hydrodynamic interactions. The results are consistent with experimental observations, showing that the radius of curvature and swimming speed depend on the cell's size and geometry. The model uses resistive-force theory to calculate the trajectory of the bacterium and provides an approximate analytical solution. The results are compared with experimental data, showing good agreement. The model also demonstrates that the bacteria's motion is influenced by the distance to the surface and the rotation rate of the flagella. The findings highlight the importance of hydrodynamic interactions in determining the motion of bacteria near solid surfaces.Swimming near solid boundaries, E. coli exhibits clockwise circular motion. This behavior is explained by a hydrodynamic model that accounts for force-free and torque-free swimming, as well as hydrodynamic interactions with the boundary. The model shows that the radius of curvature of the trajectory increases with the length of the bacterium. Experimental data on E. coli swimming near glass surfaces confirm this behavior, with the radius of curvature increasing with cell size. The model also predicts that cells swim into the surface due to hydrodynamic interactions. The results are consistent with experimental observations, showing that the radius of curvature and swimming speed depend on the cell's size and geometry. The model uses resistive-force theory to calculate the trajectory of the bacterium and provides an approximate analytical solution. The results are compared with experimental data, showing good agreement. The model also demonstrates that the bacteria's motion is influenced by the distance to the surface and the rotation rate of the flagella. The findings highlight the importance of hydrodynamic interactions in determining the motion of bacteria near solid surfaces.