diff --git a/mbta-performance/chalicelib/lamp/date.py b/mbta-performance/chalicelib/date.py
similarity index 100%
rename from mbta-performance/chalicelib/lamp/date.py
rename to mbta-performance/chalicelib/date.py
diff --git a/mbta-performance/chalicelib/historic/README.md b/mbta-performance/chalicelib/historic/README.md
new file mode 100644
index 0000000..87797b3
--- /dev/null
+++ b/mbta-performance/chalicelib/historic/README.md
@@ -0,0 +1,17 @@
+# Monthly Data Processing
+
+MBTA uploads monthly data files periodically. These monthly batches take the place of performance data when available (This may change with LAMP).
+
+## Backfill all years
+
+This should only be done if we change the processing code or need to repopulate an empty bucket
+
+```sh
+poetry run python -m mbta-performance.chalicelib.historic.backfill.main
+```
+
+### Upload to S3
+
+```sh
+aws s3 cp --recursive data/output/Events/ s3://tm-mbta-performance/Events/
+```
diff --git a/mbta-performance/chalicelib/historic/__init__.py b/mbta-performance/chalicelib/historic/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/mbta-performance/chalicelib/historic/backfill/__init__.py b/mbta-performance/chalicelib/historic/backfill/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/mbta-performance/chalicelib/historic/backfill/main.py b/mbta-performance/chalicelib/historic/backfill/main.py
new file mode 100644
index 0000000..d4e910a
--- /dev/null
+++ b/mbta-performance/chalicelib/historic/backfill/main.py
@@ -0,0 +1,39 @@
+import threading
+from ..constants import ARCGIS_IDS
+from ..download import download_historic_data, list_files_in_dir, prep_local_dir, unzip_historic_data
+from ..process import process_events
+
+
+def single_year_thread(year: str):
+    print(f"Backfilling year {year}")
+    # download the data
+    zip_file = download_historic_data(year)
+    # unzip the data
+    input_dir = unzip_historic_data(zip_file, f"data/input/{year}")
+    # process the data
+    for file in list_files_in_dir(input_dir):
+        process_events(file, "data/output")
+    print(f"Finished backfilling year {year}")
+
+
+def backfill_all_years():
+    """Backfill all years of MBTA data we can"""
+
+    prep_local_dir()
+
+    year_threads: list[threading.Thread] = []
+    for year in ARCGIS_IDS.keys():
+        year_thread = threading.Thread(
+            target=single_year_thread,
+            args=(year,),
+            name=year,
+        )
+        year_threads.append(year_thread)
+        year_thread.start()
+
+    for year_thread in year_threads:
+        year_thread.join()
+
+
+if __name__ == "__main__":
+    backfill_all_years()
diff --git a/mbta-performance/chalicelib/historic/constants.py b/mbta-performance/chalicelib/historic/constants.py
new file mode 100644
index 0000000..0c869b7
--- /dev/null
+++ b/mbta-performance/chalicelib/historic/constants.py
@@ -0,0 +1,25 @@
+ARCGIS_IDS = {
+    "2016": "3e892be850fe4cc4a15d6450de4bd318",
+    "2017": "cde60045db904ad299922f4f8759dcad",
+    "2018": "25c3086e9826407e9f59dd9844f6c975",
+    "2019": "11bbb87f8fb245c2b87ed3c8a099b95f",
+    "2020": "cb4cf52bafb1402b9b978a424ed4dd78",
+    "2021": "611b8c77f30245a0af0c62e2859e8b49",
+    "2022": "99094a0c59e443cdbdaefa071c6df609",
+    "2023": "9a7f5634db72459ab731b6a9b274a1d4",
+    "2024": "4adbec39db40498a8530496d8c63a924",
+}
+
+
+HISTORIC_COLUMNS = [
+    "service_date",
+    "route_id",
+    "trip_id",
+    "direction_id",
+    "stop_id",
+    "stop_sequence",
+    "vehicle_id",
+    "vehicle_label",
+    "event_type",
+    "event_time_sec",
+]
diff --git a/mbta-performance/chalicelib/historic/download.py b/mbta-performance/chalicelib/historic/download.py
new file mode 100644
index 0000000..7725b3f
--- /dev/null
+++ b/mbta-performance/chalicelib/historic/download.py
@@ -0,0 +1,52 @@
+import pathlib
+import requests
+import os
+from zipfile import ZipFile
+import subprocess
+from .constants import ARCGIS_IDS
+
+
+def prep_local_dir():
+    pathlib.Path("data").mkdir(exist_ok=True)
+    pathlib.Path("data/input").mkdir(exist_ok=True)
+    pathlib.Path("data/output").mkdir(exist_ok=True)
+
+
+def download_historic_data(year: str):
+    if year not in ARCGIS_IDS.keys():
+        raise ValueError(f"Year {year} dataset is not available. Supported years are {list(ARCGIS_IDS.keys())}")
+
+    url = f"https://www.arcgis.com/sharing/rest/content/items/{ARCGIS_IDS[year]}/data"
+    response = requests.get(url)
+    if response.status_code != 200:
+        raise ValueError(f"Failed to fetch historic data from {url}. Status code: {response.status_code}")
+
+    with open(f"data/input/{year}.zip", "wb") as f:
+        f.write(response.content)
+    return os.path.abspath(f"data/input/{year}.zip")
+
+
+def unzip_historic_data(zip_file: str, output_dir: str):
+    pathlib.Path(output_dir).mkdir(exist_ok=True)
+
+    try:
+        with ZipFile(zip_file, "r") as zip_ref:
+            # Extract all the contents of zip file in different directory
+            zip_ref.extractall(output_dir)
+    except NotImplementedError:
+        print("Zip file extraction failed. Likely due to unsupported compression method.")
+        print("Attempting to extract using unzip")
+        subprocess.Popen(["unzip", "-o", "-d", output_dir, zip_file])
+
+    return output_dir
+
+
+def list_files_in_dir(dir: str):
+    csv_files = []
+    files = os.listdir(dir)
+    for file in files:
+        if os.path.isfile(os.path.join(dir, file)):
+            csv_files.append(os.path.join(dir, file))
+        elif os.path.isdir(os.path.join(dir, file)):
+            csv_files += list_files_in_dir(os.path.join(dir, file))
+    return csv_files
diff --git a/mbta-performance/chalicelib/historic/process.py b/mbta-performance/chalicelib/historic/process.py
new file mode 100644
index 0000000..23efb59
--- /dev/null
+++ b/mbta-performance/chalicelib/historic/process.py
@@ -0,0 +1,41 @@
+import pandas as pd
+import pathlib
+from .constants import HISTORIC_COLUMNS
+
+
+def process_events(input_csv: str, outdir: str, nozip: bool = False):
+    df = pd.read_csv(
+        input_csv,
+        usecols=HISTORIC_COLUMNS,
+        parse_dates=["service_date"],
+        dtype={
+            "route_id": "str",
+            "trip_id": "str",
+            "stop_id": "str",
+            "vehicle_id": "str",
+            "vehicle_label": "str",
+            "event_time": "int",
+        },
+    )
+
+    df["event_time"] = df["service_date"] + pd.to_timedelta(df["event_time_sec"], unit="s")
+    df.drop(columns=["event_time_sec"], inplace=True)
+
+    service_date_month = pd.Grouper(key="service_date", freq="1M")
+    grouped = df.groupby([service_date_month, "stop_id"])
+
+    for name, events in grouped:
+        service_date, stop_id = name
+
+        fname = pathlib.Path(
+            outdir,
+            "Events",
+            "monthly-data",
+            str(stop_id),
+            f"Year={service_date.year}",
+            f"Month={service_date.month}",
+            "events.csv.gz",
+        )
+        fname.parent.mkdir(parents=True, exist_ok=True)
+        # set mtime to 0 in gzip header for determinism (so we can re-gen old routes, and rsync to s3 will ignore)
+        events.to_csv(fname, index=False, compression={"method": "gzip", "mtime": 0} if not nozip else None)
diff --git a/mbta-performance/chalicelib/historic/tests/__init__.py b/mbta-performance/chalicelib/historic/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/mbta-performance/chalicelib/lamp/ingest.py b/mbta-performance/chalicelib/lamp/ingest.py
index 49d98b2..c1ce14e 100644
--- a/mbta-performance/chalicelib/lamp/ingest.py
+++ b/mbta-performance/chalicelib/lamp/ingest.py
@@ -4,7 +4,7 @@
 import requests
 import pandas as pd
 
-from .date import format_dateint, get_current_service_date
+from ..date import format_dateint, get_current_service_date
 from .. import parallel
 from .. import s3
 
diff --git a/mbta-performance/chalicelib/tests/__init__.py b/mbta-performance/chalicelib/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/mbta-performance/chalicelib/lamp/tests/test_date.py b/mbta-performance/chalicelib/tests/test_date.py
similarity index 100%
rename from mbta-performance/chalicelib/lamp/tests/test_date.py
rename to mbta-performance/chalicelib/tests/test_date.py