Adding the two numbers, we get $53.463 + 12.9873 = 66.4503$.
Rounding to the nearest thousandth, we get $\boxed{66.450}$.The answer is: 66.450
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
Add 53.463 to 12.9873 and round to the nearest thousandth.

### Answer:
