Where a stipulator had no interest in the performance for the third party (and provided the stipulatio alteri was phrased correctly), the promisor first had to confirm the promise by oath in order to render the natural obligation into a civil obligation.
How far away is Venus from Earth? The planet Venus is the second planet from the sun and Earth is the third. Venus is the closest planet to Earth. It is about 25 million miles (40 million kilometers) away from Earth.
And that's why the Earth-Venus distance calculated in the previous paragraph (42 million kilometers) is slightly greater than the actual minimum Earth-Venus distance (38 million kilometers) - the planets' eccentric orbits can allow them to get slightly closer than the distance that one finds from the simple calculation.