Al-Masjid al-Nabawi

When the Prophet arrived at what was then Yathrib, at the end of his Hijrah journey, it was clear that he did not have a specific place in mind from among the conglomeration of settlements. He halted at a place called Quba, as a guest with one called Kulthum b. al-Hidm in the dwelling of `Amr b. `Awf staying there for 3-4 days. A mosque was built there which was later named by the Qur'an as Masjid al-Taqwa. This was the first mosque established by the Prophet.
 Masjid-Al-Nabawi
Then he mounted his camel with Abu Bakr behind him and, as he advanced he offered his Friday Prayer in the dwellings of Banu Salim b. `Awf. A hundred men were in front of him when he delivered the first Friday Sermon ever. The `Awf tribe requested him to take residence with them but he said, “Let alone the camel, for she is under command (from on High).” So he moved on. Similar requests were made by men of other dwellings, but he gave them the same answer, until she arrived at a spot where the Masjid al-Nabawi now stands. The camel squatted down at a place, then got up again, moved forward and stopped. Then she turned and came back to the first spot to settle down there for good, and the Prophet came down. It was the settlement of Banu Najjar with whom he was related from his mother’s side, the site – which served the purposes of an open camel-stable, belonged to two orphans, and the house that stood right opposite the spot was that of Abu Ayyub al-Ansari. The latter came forward and carried away the Prophet’s baggage to his house settling the issue of where he will stay.
He had not brought any of his wives with him and so stayed alone. Of course, it would not have been easy for a 53-year old person to be living alone, after a long journey, but perhaps it was because his Hijrah journey was not a pre-planned one for him to have sent his wives across in advance. That necessitated Abu Ayyub to send him meals which were accepted with grace, although he was not in the habit of accepting gifts without responding correspondingly.
 Masjid-Al-Nabawi

He stayed with Abu Ayyub for 15 days, (with Abu Bakr having found a place with one of his relatives), during which he built the mosque, the Masjid al-Nabawi, and his own quarters. He participated in the construction of the mosque, and although apparently it did not seem necessary, invited others to join in the construction (perhaps for them to share in the rewards until the Hour strikes). It was a simple hut, with a roof of frond-thatch and the floor bare sand that turned into mud when it rained.
The Prophet indicated boundaries of Madinah and, marking its boundaries, declared the town a Sanctuary like Ibrahim had declared Makkah a Sanctuary.
The Mosque has been expanded several times over since the time of the Prophet. Dajjal will lay siege to Madinah, followed by an earth-shake that will result in all unbelieving and hypocritical elements leaving the town. But Dajjal will not be able to enter the town. At every entrance to the town, he will find angels guarding it. Ultimately, he will lift the siege and leave.
The Prophet has said that a Prayer in this mosque is better than a thousand Prayers in any other mosque except the Grand Mosque at Makkah.
The size of the Mosque that the Prophet built was quite modest: about 2475 sq.m.; (that is, roughly 50x50 m., though the original was not a square). There were a few pagan graves there, and some date palm trees. The graves were cleared (perhaps dug and bones dispatched), and the trunks from the date palm trees were used at the walls. The roof was thatched and the floor was loose sand that turned into mud when it rained leaving marks on the foreheads of the devotees when they prayed while the floor was still wet. For a long time the Mosque was not lit, until one of the Companions placed a lamp and the Prophet did not object.